Control apparatus for multi-cylinder internal combustion engine and control method

ABSTRACT

A control apparatus calculates a exhaust gas air-fuel ratio of a plurality of cylinders, in which the operation angle of an intake valve is set to a predetermined operation angle, e.g., a maximum operation angle, based on a value output from an air-fuel ratio sensor so as to minimize a variation in an fuel injection quantity between the plurality of cylinders by that exhaust gas air-fuel ratio. That is, the exhaust gas air-fuel ratio of the plurality of cylinders, in which the valve opening characteristics of the intake valve and an exhaust valve are set such that the intake air amount to be introduced into the plurality of cylinders is limited by the opening amount of a throttle valve, for example, and not limited by the valve opening characteristics of the intake valve or the exhaust valve is calculated, and the variation in the fuel injection quantity among the plurality of cylinders is then reduced by that exhaust gas air-fuel ratio. Then, the variation in valve opening characteristics among the cylinders is reduced.

INCORPORATION BY REFERENCE

This is a Division of application Ser. No. 10/058,305 filed Jan. 30,2002 now U.S. Pat. No. 7,073,493. The disclosure of the priorapplication is hereby incorporated by reference herein in its entirety.The disclosures of Japanese Patent Applications No. 2001-165247 filed onMay 31, 2001, and No. 2001-028685 filed on Feb. 5, 2001, including theirspecifications, drawings and abstracts are incorporated herein byreference in their entireties.

BACKGROUND OF THE INVENTION

1. Field of Invention

The invention relates generally to control apparatus and methods for amulti-cylinder internal combustion engine.

2. Description of Related Art

Conventionally, a control apparatus for a multi-cylinder internalcombustion engine, which reduces variation in the air-fuel ratio betweencylinders is known. An example of this type of control apparatus isdisclosed in Japanese Patent Application Laid-Open Publication No.6-213044. The control apparatus disclosed in this publication calculatesthe air-fuel ratio of each of a plurality of cylinders based on a valueoutput from an air-fuel sensor. Any variation in the air-fuel ratiosbetween the cylinders is then minimized by controlling the valve liftamount of each of the cylinders.

Variation in the fuel injection quantity between cylinders, however, maylead to a variation in torque between the cylinders, which may result inpulsation. With the control apparatus disclosed in the above-mentionedpublication, it is possible that, even if a variation in air-fuel ratiobetween the cylinders is minimized, a variation in torque may stilloccur between the cylinders.

Further in the control apparatus disclosed in the foregoing publication,although variation in the air-fuel ratio between the cylinders isminimized by controlling the valve lift amount, the publicationdiscloses nothing about how to control the variation in air-fuel ratiobetween the cylinders in the event that the amount of valve overlap ofthe intake valve and the exhaust valve can be changed. Moreover, thepublication discloses nothing about how to control the variation in theair-fuel ratio between the cylinders in the event that the operationangle of the intake valve can be changed. Therefore, variation in theair-fuel ratio between the cylinders with this control apparatus is notable to be appropriately controlled both in the case where the amount ofthe valve overlap of the intake valve and the exhaust valve is able tobe changed, and in the case where the operation angle of the intakevalve is able to be changed.

SUMMARY OF THE INVENTION

In view of the foregoing problems, it is one object of the invention toprovide a control apparatus for a multi-cylinder internal combustionengine, which is capable of minimizing both a variation in the air-fuelratio between the cylinders as well as a variation in torque between thecylinders.

It is a further object of the invention to provide a control apparatusfor a multi-cylinder internal combustion engine, which is capable ofappropriately controlling the variation in the air-fuel ratio betweenthe cylinders. More specifically, it is an object of the invention toprovide a control apparatus for a multi-cylinder internal combustionengine, which is capable of appropriately controlling the variation inair-fuel ratio between the cylinders both when the amount of valveoverlap of the intake valve and the exhaust valve can be changed, aswell as when the operation angle of the intake valve can be changed.

A still further object of the invention is to provide a controlapparatus for a multi-cylinder internal combustion engine in which atarget air-fuel ratio value is able to be changed to a more appropriatevalue based on the operation angle of the intake valve than when thetarget air-fuel ratio is not corrected based on the operation angle ofthe intake valve. That is, it is an object of the invention is toprovide a control apparatus for a multi-cylinder internal combustionengine, which is capable of executing appropriate air-fuel ratiofeedback control even when a sensor is not sufficiently exposed to anexhaust gas, i.e., even when a target air-fuel ratio calculated from avalue output by a sensor is not an appropriate target air-fuel ratio.

According to one aspect of the invention, a control apparatus for amulti-cylinder internal combustion engine including a plurality ofcylinders is provided with a controller that calculates an exhaust gasair-fuel ratio of a cylinder when valve opening characteristics of anintake valve and an exhaust valve of each of the cylinders of theinternal combustion engine are set such that an amount of an intake airintroduced into the cylinder is not limited by the valve openingcharacteristics; and reduces a variation in a fuel injection quantityamong the cylinders on the basis of the calculated exhaust gas air-fuelratio of each of the cylinders.

In the control apparatus, the controller calculates the exhaust gasair-fuel ratio of each of the cylinders when the valve openingcharacteristics of the intake valve and the exhaust valve of thecylinder are set such that the amount of the intake air introduced intoeach of the cylinders of the internal combustion engine is limited by athrottle valve opening amount.

In the control apparatus, when the valve opening characteristics of theintake valve and the exhaust valve of the cylinder are set so as not tolimit the quantity of air introduced into the cylinder, the exhaust gasair-fuel ratio of the cylinder is calculated. Preferably, when the valveopening characteristics of the intake valve and the exhaust valve of thecylinder are set such that the quantity of air introduced into thecylinder is limited by the throttle valve opening amount and not limitedby the valve opening characteristics, the exhaust gas air-fuel ratio ofthe cylinder is calculated. In order to calculate an exhaust gasair-fuel ratio of each of the cylinders, the valve openingcharacteristics of the intake valve and the exhaust valve of thecylinder are set such that quantity of the intake air introduced intothe cylinder is limited by the throttle valve opening amount and notlimited by the valve opening characteristics of the intake and exhaustvalves of the cylinder. In other words, the throttle valve openingamount of one cylinder upon calculation of the exhaust gas air-fuelratio of the cylinder is made substantially equivalent to that of another cylinder upon calculation of the exhaust gas air-fuel ratio of theother cylinder so as to make the quantity of the intake air introducedinto the one cylinder upon calculation of the exhaust gas air-fuel ratioof the one cylinder equivalent to that of the other cylinder. Further inthe invention, the amount of the intake air introduced into one cylinderupon calculation of the exhaust gas air-fuel ratio of the cylinder ismade equivalent to that of the exhaust gas air fuel ratio of the othercylinder so as to obtain the exhaust gas air-fuel ratio of the cylinder.As a result, a variation in the fuel injection amount among thecylinders can be reduced on the basis of the exhaust gas air-fuel ratio.Accordingly, each amount of the intake air introduced into each of thecylinders is made equivalent, and then the respective fuel injectionquantity is corrected so as to make each exhaust gas air-fuel ratio ofthe cylinders equivalent. Unlike the control apparatus disclosed inJapanese Patent Application Laid-Open Publication No. 6-213044, thevariation in the air-fuel ratio among the cylinders is reduced whilecontrolling a variation in torque among the cylinders when there isvariation in the fuel injection quantity among the cylinders, thuspreventing pulsation. That is, the control apparatus of this aspect ofthe invention reduces a variation in the air-fuel ratio among thecylinders as well as a variation in torque among the cylinders.

According to another aspect of the invention, a control apparatus for amulti-cylinder internal combustion engine including a plurality ofcylinders is provided with a controller that calculates an exhaust gasair-fuel ratio of each of the cylinders when an operation angle of anintake valve of each of the cylinders of the internal combustion engineis set to a predetermined angle, and reduces a variation in a fuelinjection quantity among the cylinders on the basis of the calculatedexhaust gas air-fuel ratio of each of the cylinders.

In the control apparatus, the controller calculates the exhaust gasair-fuel ratio of each of the cylinders when the operation angle of theintake valve is set such that an amount of intake air introduced into acylinder of the internal combustion engine is not limited by theoperation angle of the intake valve.

In the control apparatus, the controller calculates an exhaust gasair-fuel ratio of each of the cylinders when the amount of the intakeair introduced into each of the cylinders of the internal combustionengine is not limited by the operation angle of the intake valve, but islimited by a throttle valve opening amount.

In the control apparatus, the controller calculates the exhaust gasair-fuel ratio of each of the cylinders when the operation angle of theintake valve is set to a maximum operating angle.

In the control apparatus according to another aspect of the invention,when the operation angle of the intake valve of a cylinder is set to apredetermined angle, the exhaust gas air-fuel ratio of the cylinder iscalculated. More specifically, in the control apparatus, the operationangle of the intake valve is set so as not to limit the amount of intakeair introduced into the cylinder, and then the exhaust gas air-fuelratio of that cylinder is calculated. Preferably in the controlapparatus, the operation angle of the intake valve is set such that theamount of the intake air introduced into a cylinder is limited by athrottle valve opening amount, and is not limited by the operation angleof the intake valve, and the exhaust gas air-fuel ratio of the cylinderis calculated. More preferably, the operation angle of the intake valveof a cylinder is set to a maximum angle, and the exhaust gas air-fuelratio of that cylinder is calculated. That is, the amount of the intakeair introduced into the cylinder is limited by the throttle valveopening amount, and is not limited by the operation angle of the intakevalve set to a maximum angle in order to calculate the exhaust gasair-fuel ratio of that cylinder. More specifically, the amount of theintake air introduced into one cylinder upon calculation of the exhaustgas air-fuel ratio of that cylinder can be made equivalent to that of another cylinder by making the throttle valve opening amount obtained uponcalculation of the exhaust gas air-fuel ratio of the one cylindersubstantially equivalent to that of the other cylinder.

In the control apparatus, the amount of the intake air introduced intoone cylinder upon calculation of the exhaust gas air-fuel ratio of thatcylinder is made equivalent to that of the other cylinder such that avariation in the fuel injection quantity can be minimized on the basisof the calculated exhaust gas air-fuel ratio. Accordingly, the amount ofthe intake air introduced to each of the cylinders is made equivalentand the fuel injection quantity is corrected so as to make the exhaustgas air-fuel ratio of each of the cylinders equivalent. Unlike thecontrol apparatus disclosed in Japanese Patent Application Laid-OpenPublication No. 6-213044, the variation in the air-fuel ratio among thecylinders can be reduced while controlling a variation in the torqueamong the cylinders in the presence of the variation in the fuelinjection quantity among the cylinders, thus preventing pulsation.Accordingly, the variation both in the air-fuel ratio and in the torqueamong the cylinders can be reduced.

According to another aspect of the invention, a control apparatus for amulti-cylinder internal combustion engine is provided with a controllerthat calculates an exhaust gas air-fuel ratio of each of the cylinderswhen a valve overlap amount of an intake valve and an exhaust valve ofeach of the cylinders of the internal combustion engine is set to apredetermined amount, and reduces a variation in a fuel injectionquantity among the plurality of cylinders on the basis of the calculatedexhaust gas air-fuel ratio of each of the cylinders.

In the control apparatus, the controller calculates the exhaust gasair-fuel ratio of each of the cylinders when the valve overlap amount ofthe intake valve and the exhaust valve is set such that an amount of theintake air introduced into the cylinders is not limited by the valveoverlap amount.

In the control apparatus, the controller calculates the exhaust gasair-fuel ratio of each of the cylinders when the valve overlap amount ofthe intake valve and the exhaust valve is set such that the amount ofthe intake air introduced into the cylinders is not limited by the valveoverlap amount, but is limited by a throttle valve opening amount.

In the control apparatus, the controller calculates the exhaust gasair-fuel ratio of each of the cylinders when the valve overlap amount ofthe intake valve and the exhaust valve is set to a minimum amount.

In the control apparatus according to another aspect of the invention,an exhaust gas air-fuel ratio of each of the cylinders is calculated inwhich a valve overlap amount of the intake valve and the exhaust valveis set to a predetermined amount. More specifically, the controlapparatus calculates the exhaust gas air-fuel ratio of each of thecylinders in which the overlap amount of the intake valve and theexhaust valve is set so as not to limit the quantity of air introducedinto the cylinders. Preferably, the control apparatus calculates theexhaust gas air-fuel ratio of each of the cylinders in which the valveoverlap amount of the intake valve and the exhaust valve is set suchthat the intake air amount introduced into the cylinders is limited bythe throttle valve opening amount, and is not limited by the valveoverlap amount of the intake valve and the exhaust valve. Mostpreferably, the control apparatus calculates the exhaust gas air-fuelratio of each of the cylinders in which the valve overlap amount of theintake valve and the exhaust valve is set to a minimum valve overlapamount. That is, the control apparatus calculates the exhaust gasair-fuel ratio of a certain cylinder, when the valve overlap amount ofthe intake valve and the exhaust valve is set to the minimum amount sothat the intake air amount introduced into that cylinder is limited bythe throttle valve opening amount, and is not limited by the valveoverlap amount. In other words, the intake air amount into a cylinderupon calculation of the exhaust gas air-fuel ratio of the cylinder ismade equivalent to that of the other cylinder by making the throttlevalve opening amount upon calculation of the exhaust gas air-fuel ratioof a cylinder substantially equivalent to that of the other cylinder. Inthe control apparatus, the variation in the fuel injection quantityamong cylinders can be reduced by making the intake air amount into acylinder upon calculation of the exhaust gas air-fuel ratio of thecylinder equivalent to that of the other cylinder. In other words, theintake air amount of all cylinders is made equivalent and the fuelinjection quantity is corrected so as to make all the exhaust gasair-fuel ratios of the cylinders equivalent. Unlike Japanese PatentApplication Laid-Open Publication No. 6-213044, the variation in theair-fuel ratio among the cylinders can be reduced while reducing thevariation in the torque among the cylinders in the presence of thevariation in the fuel injection quantity among the cylinders, thuspreventing pulsation. More specifically, the control apparatus iscapable of minimizing the variation both in the air-fuel ratio and thetorque among the cylinders.

In the control apparatus according to another aspect of the invention,the controller calculates an exhaust gas air-fuel ratio of each of thecylinders when the valve opening characteristics of the intake valve andthe exhaust valve are set such that the amount of the intake airintroduced into the cylinder is limited by the valve openingcharacteristics after reducing the variation in the fuel injectionquantity among the plurality of cylinders; and reduces a variation inthe valve opening characteristics of the intake valve and the exhaustvalve among the plurality of cylinders on the basis of the calculatedexhaust gas air-fuel ratio of the cylinders.

In the control apparatus, the controller calculates the exhaust gasair-fuel ratio of each of the cylinders when the valve openingcharacteristics of the intake valve and the exhaust valve are set suchthat the amount of the intake air introduced into the cylinders is notlimited by a throttle valve opening amount, but is limited by the valveopening characteristic of the intake valve and the exhaust valve afterreducing the variation in the fuel injection quantity among thecylinders.

The control apparatus according to another aspect of the inventioncalculates, after reducing the variation in the fuel injection quantityamong the cylinders, the exhaust gas air-fuel ratio of a cylinder inwhich the valve opening characteristics of the intake valve and theexhaust valve are set so as to limit the intake air amount introducedinto the cylinder, and then reduces the variation in the valve openingcharacteristics of the intake valve and the exhaust valve among thecylinders based on the set exhaust gas air-fuel ratio. More preferably,the control apparatus calculates, after reducing the variation in thefuel injection quantity among the cylinders, the exhaust gas air-fuelratio of the cylinder in which the valve opening characteristics of theintake valve and the exhaust valve are set such that the intake airamount introduced into the cylinder is limited by the valve openingcharacteristics of the intake valve or exhaust valve, and is not limitedby the throttle valve opening amount, and then reduces the variation inthe valve opening characteristics of the intake valve and the exhaustvalve among the cylinders based on the calculated exhaust gas air-fuelratio. That is, after reducing the variation in the fuel injectionquantity among the cylinders, the control apparatus changes the valveopening characteristics of the intake valve and the exhaust valve ofeach cylinder so that the exhaust gas air-fuel ratio of one cylinder ismade equivalent to that of another cylinder. The control apparatus iscapable of reducing the variation in the valve opening characteristicsof the intake valve and the exhaust valve among the cylinders withoutgenerating variation in the torque among the cylinders irrespective ofthe variation in the fuel injection quantity among the cylinders.

In the control apparatus, the controller calculates the exhaust gasair-fuel ratio of each of the cylinders when the operation angle of theintake valve is set to an operation angle that is smaller than thepredetermined operation angle after reducing the variation in the fuelinjection quantity among the cylinders, and reduces a variation in theamount of the intake air among the cylinders on the basis of thecalculated exhaust gas air-fuel ratio of each of the cylinders.

The control apparatus of the invention calculates, after reducing thevariation in the fuel injection quantity among the cylinders, theexhaust gas air-fuel ratio of each of the cylinders in which theoperation angle of the intake valve is set to an operation angle smallerthan the predetermined operation angle, and then reduces the variationin the intake air amount among the cylinders on the basis of thecalculated exhaust gas air-fuel ratio. That is, after reducing thevariation in the fuel injection quantity among the cylinders, theoperation angle of the intake valve of each cylinder is changed suchthat the exhaust gas air-fuel ratio of one cylinder is made equivalentto that of another cylinder. The control apparatus is capable ofreducing the variation in the intake air amount among the cylinderswithout generating variation in torque among the cylinders irrespectiveof the variation in the fuel injection quantity among the cylinders.

In the control apparatus, the controller calculates the exhaust gasair-fuel ratio of each of the cylinders when the operation angle of theintake valve is set to an operation angle that is smaller than thepredetermined operation angle after reducing the variation in the fuelinjection quantity among the cylinders, and reduces a variation in theoperation angle of the intake valve among the cylinders on the basis ofthe calculated exhaust gas air-fuel ratio of each of the cylinders.

The control apparatus of the invention calculates, after reducing thevariation in the fuel injection quantity among the cylinders, theexhaust gas air-fuel ratio of the cylinder in which the operation angleof the intake valve is set to an operation angle smaller than thepredetermined operation angle, and then reduces the variation in theoperation angle of the intake valve among the cylinders on the basis ofthe calculated exhaust gas air-fuel ratio. That is, after reducing thevariation in the fuel injection quantity among the cylinders, theoperation angle of the intake valve of each cylinder is changed suchthat the exhaust gas air-fuel ratio of one cylinder is made equivalentto that of another cylinder. The control apparatus is capable ofreducing the variation in the intake air amount among the cylinderswithout generating a variation in torque among the cylindersirrespective of the variation in the fuel injection quantity among thecylinders.

In the control apparatus, a neural network can be used to reduce thevariation among the cylinders.

The control apparatus of the invention preferably reduces the variationamong the cylinders using a neural network. As a result, the variationamong the cylinders can be reduced more effectively than ageneral-purpose control apparatus in which the neural network is notemployed.

According to another aspect of the invention, the control apparatus fora multi-cylinder internal combustion engine including a plurality ofcylinders is provided with a controller that reduces a variation amongthe cylinders on the basis of a valve overlap amount of an intake valveand an exhaust valve of each of the cylinders.

In the control apparatus, the controller reduces a variation in a fuelinjection quantity among the cylinders on the basis of the valve overlapamount of the intake valve and the exhaust valve of each of thecylinders.

The control apparatus of this aspect of the invention reduces thevariation among the cylinders on the basis of a valve overlap amount ofthe intake valve and the exhaust valve. More specifically, the controlapparatus reduces the variation in the fuel injection quantity among thecylinders on the basis of the valve overlap amount of the intake valveand the exhaust valve. The control apparatus of the invention is capableof reducing the variation in the air-fuel ratio among the cylinders moreeffectively when the valve overlap amount can be changed than thecontrol apparatus for a multi-cylinder internal combustion enginedisclosed in Japanese Patent Application Laid-Open Publication No.6-213044, in which the variation among the cylinders cannot be reducedon the basis of the valve overlap amount of the intake valve and theexhaust valve. In other words, the control apparatus is capable ofappropriately controlling the variation in the air-fuel ratio among thecylinders.

According to another aspect of the invention, a control apparatus for amulti-cylinder internal combustion engine including a plurality ofcylinders is provided with a controller that reduces a variation amongthe cylinders on the basis of an operation angle of an intake valve ofeach of the cylinders.

In the control apparatus, the controller reduces a variation in anair-fuel ratio among the cylinders on the basis of the operation angleof the intake valve of each of the cylinders.

The control apparatus of this aspect of the invention reduces avariation among the cylinders on the basis of an operation angle of theintake valve. More specifically, the control apparatus reduces thevariation in the air-fuel ratio among the cylinders on the basis of theoperation angle of the intake valve. Unlike the control apparatus for amulti-cylinder internal combustion engine disclosed in Japanese PatentApplication Laid-Open Publication No. 6-213044, in which a variationbetween cylinders cannot be reduced on the basis of the operation angleof the intake valve, the control apparatus of the invention is capableof reducing the variation in the air-fuel ratio among the cylindersappropriately even when the operation angle of the intake valve ischanged. The variation in the air-fuel ratio among the cylinders, thus,can be appropriately controlled.

In the control apparatus, the controller reduces a variation in theair-fuel ratio among the cylinders by correcting a fuel injectionquantity on the basis of the operation angle of the intake valve.

In the control apparatus, an amount of correction of the fuel injectionquantity is increased as the operation angle of the intake valve isdecreased.

In the control apparatus according to another aspect of the invention,the controller calculates a fuel injection quantity correctioncoefficient for reducing the variation in the air-fuel ratio when thevariation in the air-fuel ratio among the cylinders is detected,calculates a relationship between the calculated fuel injection quantitycorrection coefficient and the operation angle of the intake valveobtained upon calculation of the fuel injection quantity correctioncoefficient, and updates the fuel injection quantity correctioncoefficient when the operation angle of the intake valve is changed onthe basis of the changed operation angle and the calculatedrelationship.

In the control apparatus, the fuel injection quantity correctioncoefficient changes relative to the operation angle of the intake valvesuch that an amount of correction of the fuel injection quantity isincreased as the operation angle is decreased.

The control apparatus as described above reduces the variation in theair-fuel ratio among the cylinders by correcting the fuel injectionquantity on the basis of the operation angle of the intake valve. Forexample, when the air-fuel ratio of one cylinder varies on the richside, the fuel injection quantity supplied to the cylinder is decreasedso as to reduce the variation in the air-fuel ratio among the cylinders.Also, the smaller the operation angle of the intake valve becomes, thegreater the variation in the air-fuel ratio becomes among the cylinderswhen the actual operation angle deviates from the target operationangle. In view of this, the variation in the air-fuel ratio among thecylinders can be reduced by executing correction, for example,increasing the fuel injection quantity as the operation angle of theintake valve becomes smaller. This allows the variation in the air-fuelratio among the cylinders to be controlled more appropriately than whenthe fuel injection quantity is not corrected on the basis of theoperation angle of the intake valve. More specifically, when a variationin the air-fuel ratio among the cylinders is detected, the controlapparatus calculates a fuel injection quantity correction coefficientfor reducing such variation, and also calculates a relationship betweenthe calculated fuel injection quantity correction coefficient and theoperation angle of the intake valve upon calculation of the fuelinjection quantity correction coefficient. When the operation angle ofthe intake valve has changed, the control apparatus then updates thefuel injection quantity correction coefficient on the basis of thechanged operation angle of the intake valve and the calculatedrelationship. The relationship between the fuel injection quantitycorrection coefficient and the operation angle of the intake valve canbe represented by a relation formula or a map, for example.

According to another aspect of the invention, a control apparatus for amulti-cylinder internal combustion engine including a plurality ofcylinders is provided with a controller that corrects a coefficient foran air-fuel ratio feedback control to a predetermined coefficient on thebasis of an operation angle of an intake valve of each of the cylinders,wherein a number of sensors provided in the internal combustion enginefor detecting an air-fuel ratio or an oxygen concentration is smallerthan a number of the cylinders of the internal combustion engine.

In the control apparatus, the coefficient for the air-fuel ratiofeedback control is corrected to the predetermined coefficient such thata target air-fuel ratio is increased as the operation angle of theintake valve is decreased.

According to another aspect of the invention, a control apparatus for amulti-cylinder internal combustion engine including a plurality ofcylinders is provided with a controller that corrects a target air-fuelratio on the basis of an operation angle of an intake valve of each ofthe cylinders, wherein a number of sensors provided in the internalcombustion engine for detecting an air-fuel ratio or an oxygenconcentration is smaller than a number of each of the cylinders of theinternal combustion engine.

In the control apparatus, the target air-fuel ratio is corrected suchthat an amount for correcting the target air-fuel ratio is increased asthe operation angle of the intake valve is decreased.

According to another aspect of the invention, the controller calculatesthe target air-fuel ratio when a variation in the air-fuel ratio amongthe cylinders is detected, calculates a relationship between the targetair-fuel ratio and the operation angle of the intake valve on the basisof the calculated target air-fuel ratio and the operation angle of theintake valve obtained upon detection of the variation in the air-fuelratio; and updates the target air-fuel ratio when the operation angle ofthe intake valve is changed on the basis of the changed operation angleof the intake valve and the calculated relationship between the targetair-fuel ratio and the operation angle of the intake valve of thecylinder.

The control apparatus of the invention corrects a predeterminedcoefficient relating to an air-fuel ratio feedback control on the basisof the operation angle of the intake valve. More specifically, thecontrol apparatus corrects the target air-fuel ratio on the basis of theoperation angle of the intake valve. For example, in the event that theoverall air-fuel ratio shifts over to the rich side as a result of thetarget air-fuel ratio not being set appropriately due to the fact thatthe sensor is not sufficiently exposed to the gas, the control apparatusthen corrects the target air-fuel ratio so as to shift the overallair-fuel ratio toward the lean side. Also, when the actual operationangle of the intake valve deviates from the target operation angle, thetarget air-fuel ratio that is set on the basis of a value output by thesensor is likely to largely deviate from the appropriate target air-fuelratio as the operation angle of the intake valve becomes smaller. Inview of this fact, for example, the correction amount for the targetair-fuel ratio is increased as the operation angle of the intake valvebecomes smaller. This allows the value of the target air-fuel ratio tobe made more appropriate than when the target air-fuel ratio is notcorrected on the basis of the operation angle of the intake valve. Thatis, the control apparatus is capable of executing appropriate air-fuelratio feedback control even when a sensor is not sufficiently exposed tothe exhaust gas, i.e., even when a target air-fuel ratio calculated froma value output by a sensor is not an appropriate target air-fuel ratio.More specifically, when a variation in the air-fuel ratio among thecylinders is detected, the control apparatus calculates a targetair-fuel ratio (corrects it to an appropriate target air-fuel ratio),and also calculates a relationship between that target air-fuel ratioand the operation angle of the intake valve obtained at that time. Whenthe operation angle of the intake valve changes, the control apparatusthen calculates the appropriate target air-fuel ratio on the basis ofthe changed operation angle of the intake valve and the calculatedrelationship. The relationship between the target air-fuel ratio and theoperation angle of the intake valve can be represented by a relationalexpression or a map, for example.

In the control apparatus, the controller reduces a variation in theair-fuel ratio among the cylinders by correcting a fuel injectionquantity of each of the cylinders independently when an amount ofcorrection of the calculated fuel injection quantity is smaller than apredetermined value, and guards the amount for correcting the calculatedfuel injection quantity, corrects the target air-fuel ratio, anduniformly corrects each of the fuel injection quantity of all thecylinders on the basis of the corrected target air-fuel ratio when anamount of correction of the calculated fuel injection quantity is largerthan the predetermined value.

In view of the possibility that a large correction amount for the fuelinjection quantity might result in a variation in torque, the controlapparatus of the invention minimizes the variation in the air-fuel ratiobetween cylinders by individually correcting the fuel injection quantityin each of the cylinders when a calculated correction amount for thefuel injection quantity is small, and guards the calculated correctionamount for the fuel injection quantity with a predetermined value whenthe correction amount for the fuel injection quantity is large. At thesame time, the control apparatus also corrects the target air-fuel ratioand then uniformly corrects the fuel injection quantity of all of thecylinders on the basis of that target air-fuel ratio. Accordingly theair-fuel ratio can be appropriately controlled while minimizing thevariation in torque.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in conjunction with the followingdrawings, in which like reference numerals refer to similar elements,and wherein:

FIG. 1 is a schematic block diagram of a control apparatus for aninternal combustion engine according to an embodiment of the invention;

FIG. 2 is a detailed view of an intake system and the like of thecontrol apparatus for an internal combustion engine shown in FIG. 1;

FIG. 3 is a plan view of an intake system and the like of the controlapparatus for an internal combustion engine shown in FIG. 2;

FIG. 4 is a detailed view of a cam and cam shaft for the intake valveshown in FIG. 1;

FIG. 5 is a detailed view of the apparatus and the like for changing avalve lift amount;

FIG. 6 is a graph showing the change in the valve lift amount of theintake valve following operation of an apparatus for changing the valvelift amount;

FIG. 7 is a detailed view of the apparatus and the like for shifting anopening and closing timing of the intake valve shown in FIG. 1;

FIG. 8 is a graph showing the shift in the opening and closing timing ofthe intake valve following operation of the apparatus for shifting theopening and closing timing of the intake valve;

FIG. 9 is a detailed view of an intake system and the like of thecontrol apparatus for another type of internal combustion engineaccording to an embodiment of the invention;

FIG. 10 is a detailed view of an intake system and the like of thecontrol apparatus for an internal combustion engine according to a thirdembodiment;

FIG. 11 is a flow chart showing a method for learning fuel injectionquantity variation according to the first and second embodiments, aswell as modifications thereof;

FIG. 12 is a flow chart showing a method for learning intake valveoperation angle variation according to the second embodiment, as well asa modification thereof;

FIG. 13 is a flow chart showing a method for learning intake valveoperation angle variation according to the first and second embodiments,as well as modifications thereof;

FIG. 14 is a flow chart showing a method for learning fuel injectionquantity variation according to a fourth embodiment through a sixthembodiment, as well as modifications thereof;

FIG. 15 is a flow chart showing a method for learning valve overlapamount variation according to the sixth embodiment, as well as amodification thereof;

FIG. 16 is a flow chart showing a method for learning valve overlapamount variation according to the fourth and fifth embodiments, as wellas modifications thereof;

FIG. 17 is a schematic block diagram of a control apparatus for aninternal combustion engine according to a seventh embodiment;

FIG. 18 is a flow chart showing a method for controlling so as tominimize variation between cylinders according to an eighth embodiment;

FIG. 19 is a graph showing a relationship between the fuel injectionquantity correction coefficient and the operation angle of an intakevalve;

FIG. 20 is a flow chart showing a method for controlling so as tocorrect the target air-fuel ratio according to a ninth embodiment;

FIG. 21 is a graph showing a relationship between the target air-fuelratio and the operation angle of an intake valve; and

FIG. 22 is a flow chart showing a method for controlling so as tominimize variation between cylinders according to a tenth embodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter embodiments of the invention will be described withreference to the attached drawings.

FIGS. 1 through 3, which illustrate an embodiment of the invention forcontrolling a first type of an internal combustion engine 1, show anintake valve 2, an exhaust valve 3, a cam 4 for opening and closing theintake valve 2, a cam 5 for opening and closing the exhaust valve 3, acam shaft 6 which supports the cam 4, and a cam shaft 7 which supportsthe cam 5. As shown in FIG. 4, the cam profile of the cam 4 according tothis exemplary embodiment is modified in the direction along the centralaxis of the cam shaft, i.e., the left end of the nose of the first cam 4in the figure is higher than the right end thereof. This feature may beutilized to change the valve lift amount of the intake valve 2 dependingon the contact between the valve lifter and one end of the cam 4. Thatis, when the valve lifter contacts the right end of the cam 4, the valvelift amount will become smaller than the valve lift amount obtained whenthe valve lifter contacts the left end of the cam 4.

FIGS. 1 through 3 also show a combustion chamber 8 formed in a cylinderand a valve lift amount changing device 9 for shifting the cam 4 in thedirection along the central axis of the cam shaft with respect to theintake valve 2 to change the valve lift amount. That is, operating thevalve lift amount changing device 9 brings the left or right end (inFIG. 4) of the cam 4 into contact with the valve lifter selectively.Changing the valve lift amount of the intake valve 2 by the valve liftamount changing device 9 consequentially changes the open area of theintake valve 2. The intake valve 2 according to this exemplaryembodiment is structured such that the open area of the intake valve 2increases as the valve lift amount increases. FIGS. 1 through 3 alsoshow a driver 10 for driving the valve lift amount changing device 9 andan opening/closing timing shift device 11 for shifting theopening/closing timing of the intake valve 2 regardless of a change inthe open period thereof. That is, operation of the opening/closingtiming shift device 11 enables the opening/closing timing of the intakevalve 2 to be shifted to the advance side or the retard side. Thefigures also show an oil control valve 12 for controlling an oilpressure for operating the opening/closing timing shift device 11. Boththe valve lift amount changing device 9 and the opening/closing timingshift device 11 are included in the variable valve train in thisexemplary embodiment.

FIGS. 1 through 3 also show a crank shaft 13, an oil pan 14, a fuelinjection valve 15, a first sensor 16 for detecting both a valve liftamount and an opening/closing timing shift amount of the intake valve 2,a second sensor 17 for detecting an engine speed, an intake pipepressure sensor 18 for detecting a pressure within an intake pipe thatsupplies intake air to the cylinder, an airflow meter 19, a coolanttemperature sensor 20 for detecting a temperature of a coolant in theinternal combustion engine 1, an intake air temperature sensor 21 fordetecting a temperature within the intake pipe for intake air to besupplied to the cylinder, an ECU (electronic control unit) 22, acylinder 50, intake pipes 51 and 52, a surge tank 53, an exhaust pipe54, a spark plug 55, a throttle valve 56, the opening amount of whichchanges regardless of the accelerator pedal operation amount, and anair-fuel ratio sensor 57 for detecting an exhaust gas air-fuel ratio.

FIG. 5 shows a magnetic body 30 connected to the cam shaft 6, a coil 31for urging the magnetic body 30 to the left, and a compression spring 32for urging the magnetic body 30 to the right. As the amount of currentpassing through the coil 31 increases, the amount by which the cam 4 andthe cam shaft 6 shift to the left increases and the valve lift amount ofthe intake valve 2 decreases.

As shown in FIG. 6, the valve lift amount of the intake valve 2increases as the amount of current passing through the coil 31 decreases(solid line→broken line→chain line). Further in this exemplaryembodiment, the closed period of the intake valve 2 also changes as thevalve lift amount changing device 9 is operated. That is, the operationangle of the intake valve 2 also changes. More specifically, theoperation angle of the intake valve 2 increases as the valve lift amountof the intake valve 2 increases (solid line→broken line→chain line).Moreover in this embodiment, the timing at which the valve lift amountof the intake valve 2 is at its peak also changes as the valve liftamount changing device 9 is operated. More specifically, the timing atwhich the valve lift amount of the intake valve 2 is at its peak isretarded as the valve lift amount of the intake valve 2 increases (solidline→broken line→chain line).

FIG. 7 shows an advance side oil passage 40 for shifting theopening/closing timing of the intake valve 2 to the advance side, aretard side oil passage 41 for shifting the opening/closing timing ofthe intake valve 2 to the retard side, and an oil pump 42. Theopening/closing timing of the intake valve 2 shifts to the advance sideas the oil pressure within the advance side oil passage 40 increases.That is, the rotation phase of the cam shaft 6 is advanced with respectto the crank shaft 13. Conversely, the opening/closing timing of theintake valve 2 shifts to the retard side as the oil pressure within theretard side oil passage 41 increases. That is, the rotation phase of thecam shaft 6 is retarded with respect to the crank shaft 13.

As shown in FIG. 8, the opening/closing timing of the intake valve 2shifts to the advance side as the oil pressure within the advance sideoil passage 40 increases (solid line→broken line→chain line). At thistime, the open period of the intake valve 2 does not change, i.e., thelength of the period during which the intake valve 2 is open does notchange.

In FIG. 9, reference numerals that are the same as those in FIGS. 1through 8 represent the same or like parts as those shown in FIGS. 1through 8. In this embodiment for controlling a second type of internalcombustion engine, the cam for driving the exhaust valve has generallythe same configuration as the cam 4 shown in FIG. 4. FIG. 9 also shows avalve lift amount changing device 9′ for shifting the cam for drivingthe exhaust valve in the direction along the central axis of the camshaft with respect to the exhaust valve 3 to change the valve liftamount of the exhaust valve 3. This valve lift amount changing device 9′has generally the same configuration as the valve lift amount changingdevice 9. FIG. 9 also shows an opening/closing timing shift device 11′for shifting the opening/closing timing of the exhaust valve 3regardless of the open period of the exhaust valve 3. Thisopening/closing timing shift device 11′ has generally the sameconfiguration as the opening/closing timing shift device 11.

In FIG. 10, which illustrates an embodiment for controlling a third typeof internal combustion engine 2, reference numerals that are the same asthose in FIGS. 1 through 8 represent the same or like parts as thoseshown in FIGS. 1 through 8. FIG. 10 also shows an intake valve drivingdevice 58 which is capable of driving individual intake valves 2 (referto FIG. 3) independently, e.g., an electromagnetic driving type intakevalve driving device, and an exhaust valve driving device 58′ which iscapable of driving individual exhaust valves 3 (refer to FIG. 3)independently, e.g., an electromagnetic driving type exhaust valvedriving device.

In modifications of the foregoing exemplary embodiments, the throttlevalve 56 may be eliminated.

In the foregoing exemplary embodiments and modifications thereof, whenthe air-fuel ratio of a cylinder among a plurality of cylinders Nos. 1through 4, is calculated based on a value output from the air-fuel ratiosensor 57 and the valve lift amount of the intake valve 2 and/or exhaustvalve 3 of each cylinder is controlled, a variation in the air-fuelratio between cylinders is able to be reduced. If variation in the fuelinjection quantity exists between cylinders, however, even if thevariation in the air-fuel ratio between cylinders is reduced, avariation in torque between cylinders is generated, resulting in apulsation (torque variation). Therefore, according to the first andsecond exemplary embodiments and modifications thereof, control such asthat to be described later is performed to both reduce variation in theair-fuel ratio between cylinders and reduce variation in the torquebetween cylinders.

A routine according to a method for learning fuel injection quantityvariation according to the foregoing embodiments and modificationthereof as shown in FIG. 11 is performed at predetermined intervals. Asshown in the figure, when this routine starts, it is determined in Step100 whether the operation angle of the intake valve 2 is at its maximum,as illustrated by the chain line in FIG. 6, for example. When the abovedetermination is “NO”, i.e., when the operation angle of the intakevalve 2 is relatively small, such that the open area of the intake valve2 is relatively small, the intake air amount to be introduced into thecylinder 50 is determined based on the open area of the intake valve 2.In the event that variation in the operation angle of the intake valve 2among cylinders exists temporarily, the intake air amount varies amongcylinders and it is determined that learning variation in the fuelinjection quantity is not possible and the routine ends. Meanwhile, whenthe determination in Step 100 is “YES”, then the intake air amount to beintroduced into the cylinder 50 is determined based on the openingamount of the throttle valve 56 or the cross-sectional area of theportion of the intake pipes 51 and 52 having the smallest internalcircumference. Even if variation in the operation angle of the intakevalve 2 exists among cylinders, it is determined that the intake airamount does not vary among cylinders, and the process proceeds to Step101.

In Step 101, it is determined whether it is time to calculate theexhaust gas air-fuel ratio of the specified cylinder No. N among aplurality of cylinders Nos. 1 through 4. When the determination is “NO”,the routine ends. When the determination is “YES”, the process proceedsto Step 102. In Step 102, the exhaust gas air-fuel ratio of the cylinderNo. N, for example, is detected for several cycles and the mean air-fuelratio thereof is calculated. This mean air-fuel ratio calculation isperformed for all of the cylinders Nos. 1 through 4. Next, in Step 103,the variation ΔQn in the fuel injection quantity among the cylinders iscalculated using the air-fuel ratio of each of the cylinders Nos. 1through 4 calculated in Step 102 on the assumption that the intake airamounts to be introduced into each of the cylinders Nos. 1 through 4 areall the same.

Next in Step 104, a variation rate Qrate-n of the fuel injectionquantity is calculated based on the variation ΔQn in the fuel injectionquantity between the cylinders calculated in Step 103. Then in Step 105,the fuel injection quantity of each of the cylinders Nos. 1 through 4 iscorrected so as to eliminate or reduce the variation in the fuelinjection quantity among the cylinders.

In the aforementioned case, when it is determined in Step 100 that theoperation angle of the intake valve 2 is set to the maximum operationangle, the exhaust gas air-fuel ratio of that cylinder is thencalculated in Step 102. That is, when it is determined in Step 100 thatthe operation angle of the intake valve 2 is set such that the intakeair amount introduced into the cylinder is not limited by the operationangle of the intake valve 2, the exhaust gas air-fuel ratio of thatcylinder is then calculated in Step 102. More specifically, when it isdetermined in Step 100 that the operation angle of the intake valve 2 isset such that the intake air amount introduced into the cylinder islimited by the opening amount of the throttle valve 56, and not limitedby the operation angle of the intake valve 2, the exhaust gas air-fuelratio of that cylinder is calculated in Step 102. In other words, forthe exhaust gas air-fuel ratio of a cylinder to be calculated in Step102, the operation angle of the intake valve 2 is set, in a step whichis not shown, such that the intake air amount introduced into thatcylinder is limited by the opening amount of the throttle valve 56, andis not limited by the operation angle of the intake valve 2. That is, bymaking the opening amount of the throttle valve 56 when the exhaust gasair-fuel ratio of the first cylinder No. 1 is calculated and the openingamount of the throttle valve 56 when the exhaust gas air-fuel ratios ofthe other cylinders Nos. 2 through 4 are calculated substantially thesame, it is possible to make the intake air amount to be introduced intothe first cylinder No. 1 when the exhaust gas air-fuel ratio thereof iscalculated and the intake air amount introduced into the other cylindersNos. 2 through 4 when the exhaust gas air-fuel ratios thereof arecalculated the same.

Further, according to the foregoing embodiments, when it is determinedin Step 100 that the intake air amount to be introduced into thecylinder No. 1 upon calculation of the exhaust gas air-fuel ratio is thesame as that to be introduced into the other cylinders Nos. 2 through 4upon calculation of the exhaust gas air-fuel ratios, variation in thefuel injection quantity among the cylinders is minimized in Step 105 bythe exhaust gas air-fuel ratio. That is, after making the intake airamount in all of the cylinders the same, the fuel injection quantity iscorrected such that the exhaust gas air-fuel ratios in all of thecylinders are the same. This makes it possible to reduce both thevariation in the air-fuel ratio among cylinders and the variation in thetorque among cylinders.

In other words, according to the embodiments, when it is determined inStep 100 that the valve opening characteristics of the intake valve 2are set such that the intake air amount to be introduced into thecylinder is limited by the opening amount of the throttle valve 56, andnot limited by the valve opening characteristics of the intake valve 2,the exhaust gas air-fuel ratio of that cylinder is then calculated inStep 102. That is, for the exhaust gas air-fuel ratio of a cylinder tobe calculated in Step 102, the valve opening characteristics of theintake valve 2 are set, in a step which is not shown, such that theintake air amount to be introduced into that cylinder is limited by theopening amount of the throttle valve 56, and is not limited by the valveopening characteristics of the intake valve 2.

Also according to modifications of the aforementioned embodiments inwhich the throttle valve 56 is not provided, when it is determined inStep 100 that the operation angle of the intake valve 2 is set to themaximum operation angle, the exhaust gas air-fuel ratio of that cylinderis calculated in Step 102. That is, when it is determined in Step 100that the operation angle of the intake valve 2 is set so as not to limitthe intake air amount to be introduced into the cylinder, the exhaustgas air-fuel ratio of that cylinder is then calculated in Step 102. Morespecifically, when it is determined in Step 100 that the operation angleof the intake valve 2 is set such that the intake air amount to beintroduced into the cylinder is limited by the cross-sectional area of aportion of the intake pipes 51 and 52 having the smallest internalcircumference, and is not limited by the operation angle of the intakevalve 2, the exhaust gas air-fuel ratio of that cylinder is thencalculated in Step 102. In other words, for the exhaust gas air-fuelratio of a cylinder to be calculated in Step 102, the operation angle ofthe intake valve 2 is set, in a step (not shown) to the maximumoperation angle such that the intake air amount to be introduced intothe cylinder is limited by the cross-sectional area of a portion of theintake pipes 51 and 52 having the smallest internal circumference, andnot limited by the operation angle of the intake valve 2.

In other words, according to the above-described modifications, when itis determined in Step 100 that the valve opening characteristics of theintake valve 2 are set such that the intake air amount to be introducedinto the cylinder is limited by the cross-sectional area of a portion ofthe intake pipes 51 and 52 having the smallest internal circumference,and not limited by the valve opening characteristics of the intake valve2, the exhaust gas air-fuel ratio of that cylinder is calculated in Step102. That is, for the exhaust gas air-fuel ratio of a cylinder to becalculated in Step 102, the valve opening characteristics of the intakevalve 2 are set, in a step (not shown) such that the intake air amountto be introduced into that cylinder is limited by the cross-sectionalarea of a portion of the intake pipes 51 and 52 having the smallestinternal circumference, and is not limited by the valve openingcharacteristics of the intake valve 2.

Also according to the exemplary embodiments and modifications thereof,the variation among cylinders is able to be reduced based on theoperation angle of the intake valve. More specifically, the variation inthe fuel injection quantity among cylinders can be reduced by theoperation angle of the intake valve. Even more specifically, when it isdetermined in Step 100 in FIG. 11 that the operation angle of the intakevalve assumes a maximum value, the variation in the fuel injectionquantity between the cylinders is minimized in Step 105. Therefore, whenit is possible to change the operation angle of the intake valve, it ispossible to control the variation in the air-fuel ratio between thecylinders more appropriately than when the variation between cylindersis not controlled by the operation angle of the intake valve. In otherwords, it is possible to appropriately control the variation in theair-fuel ratio among the cylinders.

A routine according to the method for learning intake valve operationangle variation, according to the embodiment for controlling the thirdtype of the internal combustion engine and a modification thereof shownin FIG. 12 is executed at predetermined intervals, just as the routineshown in FIG. 11. In FIG. 12, when this routine starts, it is firstdetermined in Step 150 whether the correction control in Step 105 inFIG. 11 has been completed. If the correction of the fuel injectionquantity for all of the cylinders is not yet complete, then it isdetermined that the variation in the operation angle of the intake valve2 among the cylinders can not be reduced and the routine ends. If thecorrection of the fuel injection quantity for all of the cylinders iscomplete, then the process proceeds to Step 151. In Step 151, it isdetermined whether the operation angle of the intake valve 2 is equal toor less than a predetermined threshold value. That is, it is determinedwhether the operation angle of the intake valve 2 is set to a relativelysmall value such that the intake air amount to be introduced into thecylinder is limited by the operation angle of the intake valve 2, andnot limited by the opening amount of the throttle valve 56. If thedetermination is “NO”, the routine ends. If the determination is “YES”,the process proceeds to Step 152.

In Step 152, it is determined whether it is time to calculate theexhaust gas air-fuel ratio of the specified cylinder, for example,cylinder No. N, among the plurality of cylinders Nos. 1 through 4. Ifthe determination is “NO”, the routine ends. If the determination is“YES”, the process proceeds to Step 153. In Step 153, the exhaust gasair-fuel ratio of the cylinder No. N is detected for several cycles andthe mean air-fuel ratio thereof is calculated. This mean air-fuel ratiocalculation is performed for all of the cylinders Nos. 1 through 4. Nextin Step 154, the variation ΔQ in the intake air amount among thecylinders is calculated using the air-fuel ratio of each of thecylinders Nos. 1 through 4 calculated in Step 153 on the assumption thatthe fuel injection quantity of each of the cylinders Nos. 1 through 4 isthe same.

Next in Step 155, the variation ΔAng in the operation angle of theintake valve 2 of a specified cylinder, for example, cylinder No. N, iscalculated based on the variation ΔQ in the intake air amount among thecylinders calculated in Step 154. This calculation of the variation ΔAngin the operation angle of the intake valve 2 is performed for all of thecylinders Nos. 1 through 4. Next in Step 156, the intake valve drivingdevice 58 corrects the operation angle of the intake valve 2 of each ofthe cylinders Nos. 1 through 4 such that the variation in the operationangle of the intake valves 2 among the cylinders is reduced, i.e., suchthat the variation in the intake air amount among the cylinders isreduced.

According to the embodiment for controlling the third type of theinternal combustion engine, after reducing the variation in the fuelinjection quantity between the cylinders in Step 105 in FIG. 11, when itis determined in Step 151 that the valve opening characteristics of theintake valve 2 are set so that the intake air amount to be introducedinto the cylinder is limited by the valve opening characteristics of theintake valve 2, and not limited by the opening amount of the throttlevalve 56, the process proceeds to Step 153. In Step 153, the exhaust gasair-fuel ratio of that cylinder is calculated and then in Step 156 thevariation in the valve opening characteristics of the intake valve 2among cylinders is reduced by that exhaust gas air-fuel ratio. That is,after reducing the variation in the fuel injection quantity among thecylinders, the valve opening characteristics of the intake valve 2 ofeach of the cylinders Nos. 1 through 4 are changed such that the exhaustgas air-fuel ratio of the cylinder No. 1 and the exhaust gas air-fuelratios of the other cylinders Nos. 2 through 4 are the same. Therefore,even if there is variation in the fuel intake quantity among thecylinders, no variation in torque among cylinders is generated andvariation in the valve opening characteristics of the intake valve 2among the cylinders can be reduced.

Also, according to a modification of the embodiment, after reducing thevariation in the fuel injection quantity among the cylinders in Step 105in FIG. 11, when it is determined in Step 151 that the valve openingcharacteristics of the intake valve 2 are set so that the intake airamount to be introduced into the cylinder is limited by the valveopening characteristics of the intake valve 2, and not limited by thecross-sectional area of the portion of the intake pipes 51 and 52 havingthe smallest internal circumference, the process proceeds to Step 153.In Step 153, the exhaust gas air-fuel ratio of that cylinder iscalculated and then in Step 156, the variation in the valve openingcharacteristics of the intake valve 2 among cylinders is reduced by thatexhaust gas air-fuel ratio. That is, after reducing the variation in thefuel injection quantity among the cylinders, the valve openingcharacteristics of the intake valve 2 of each of the cylinders Nos. 1through 4 are changed such that the exhaust gas air-fuel ratio of thecylinder No. 1 and the exhaust gas air-fuel ratios of the othercylinders Nos. 2 through 4 are the same. Therefore, even if there isvariation in the fuel intake quantity among cylinders, no variation intorque among cylinders is generated and the variation in the valveopening characteristics of the intake valves 2 among the cylinders canbe reduced.

More specifically, according to the embodiment for controlling the thirdtype of the internal combustion engine and the modification thereof,after reducing the variation in the fuel injection quantity among thecylinders in Step 105 in FIG. 11, when it is determined in Step 151 thatthe operation angle of the intake valve 2 is set to a predeterminedangle which is smaller than the maximum operation angle, the processproceeds to Step 153. In Step 153, the exhaust gas air-fuel ratio iscalculated and then in Step 156, the variation in the operation angle ofthe intake valve 2 among the cylinders is reduced by that exhaust gasair-fuel ratio. That is, after reducing the variation in the fuelinjection quantity among the cylinders, the operation angle of theintake valve 2 of each of the cylinders Nos. 1 through 4 is changed suchthat the exhaust gas air-fuel ratio of the cylinder No. 1 and theexhaust gas air-fuel ratios of the other cylinders Nos. 2 through 4 arethe same. Therefore, even if there is variation in the fuel intakequantity among cylinders, no variation in torque among cylinders isgenerated and the variation in the operation angle of the intake valve 2among the cylinders can be reduced.

According to the foregoing embodiment and the modification thereof,after reducing the variation in the fuel injection quantity among thecylinders in Step 105 in FIG. 11, when it is determined in Step 151 thatthe operation angle of the intake valve 2 is set to a predeterminedoperation angle that is smaller than the maximum operation angle, theprocess proceeds to Step 153. In Step 153, the exhaust gas air-fuelratio is calculated and then in Step 156, the variation in the intakeair amount among cylinders is reduced by that exhaust gas air-fuelratio. That is, after reducing the variation in the fuel injectionquantity among the cylinders, the operation angle of the intake valve 2of each of the cylinders Nos. 1 through 4 is changed such that theexhaust gas air-fuel ratio of the cylinder No. 1 and the exhaust gasair-fuel ratios of the other cylinders Nos. 2 through 4 are the same.Therefore, even if there is variation in the fuel intake quantity amongthe cylinders, no variation in torque among cylinders is generated andthe variation in the intake air amount among the cylinders can bereduced.

Also according to the embodiments for controlling the first to the thirdtype of the internal combustion engines and modifications thereof, avariation among cylinders is reduced by the operation angle of theintake valve. More specifically, when it is determined in Step 151 inFIG. 12 that the operation angle of the intake valve 2 is equal to orless than a predetermined threshold value, the variation in theoperation angle of the intake valve 2 among the cylinders is reduced inStep 156. Therefore, when it is possible to change the operation angleof the intake valve, the variation in the air-fuel ratio among thecylinders can be controlled more appropriately than when the variationin the operation angle of the intake valve 2 among the cylinders iscontrolled irrespective of the aforementioned threshold value. In otherwords, it is possible to appropriately control the variation in theair-fuel ratio among the cylinders.

A routine according to the method for learning intake valve operationangle variation, according to the embodiment for controlling the firstand the second type of the internal combustion engines and modificationsthereof, shown in FIG. 13 is executed at predetermined intervals, justas is the routine shown in FIG. 11. As shown in FIG. 13, when thisroutine starts, it is first determined in Step 150 whether the controlfor reducing the variation in the fuel injection quantity in Step 105shown in FIG. 11 has been completed, just as in FIG. 12. If the controlis not yet complete, it is determined that the variation in theoperation angle of the intake valve 2 among the cylinders can not bereduced. Accordingly the routine ends. If the correction of the fuelinjection quantity for all of the cylinders is complete, the processproceeds to Step 151. In Step 151, just as in FIG. 12, it is determinedwhether the operation angle of the intake valve 2 is equal to or lessthan a predetermined threshold value. If the determination is “NO”, theroutine ends. If the determination is “YES”, the process proceeds toStep 152.

In Step 152, it is determined whether it is time to calculate theexhaust gas air-fuel ratio of the specified cylinder, for example, thecylinder No. N, among a plurality of cylinders Nos. 1 through 4, just asin FIG. 12. If the determination is “NO”, the routine ends. If thedetermination is “YES”, the process proceeds to Step 153. In Step 153,the exhaust gas air-fuel ratio of the cylinder No. N, for example, isdetected for several cycles and the mean air-fuel ratio thereof iscalculated, just as in FIG. 12. Next in Step 154, the variation ΔQ inthe intake air amount among the cylinders is calculated using theair-fuel ratio of each of the cylinders Nos. 1 through 4 calculated inStep 153 on the assumption that the fuel injection quantity in each ofthe cylinders Nos. 1 through 4 are all the same, also just as in FIG.12.

Next in Step 250, the fuel injection quantity of each cylinder iscorrected based on the variation ΔQ in the intake air amount among thecylinders calculated in Step 154 such that the torque of all of thecylinders Nos. 1 through 4 is the same. Then in Step 251, the ignitiontiming of each cylinder is corrected based on the variation ΔQ in theintake air amount among the cylinders calculated in Step 154 such thatthe torque of all of the cylinders Nos. 1 through 4 is the same. Forexample, the ignition timing in a cylinder in which the intake airamount is relatively large is retarded during operation under high loadof the engine, in which knocking tends to occur.

According to the embodiment for controlling the first and second type ofthe internal combustion engines, after reducing the variation in thefuel injection quantity among the cylinders in Step 105 shown in FIG.11, when it is determined in Step 151 shown in FIG. 13 that the valveopening characteristics of the intake valve 2 are set such that theintake air amount to be introduced into the cylinder is limited by thevalve opening characteristics of the intake valve 2, and not limited bythe opening amount of the throttle valve 56, the process proceeds toStep 153. In Step 153, the exhaust gas air-fuel ratio of that cylinderis calculated and then in Step 250 and Step 251, the fuel injectionquantity and the ignition timing, respectively, are corrected so as toreduce the variation in torque among cylinders.

According to the foregoing embodiments and modifications thereof, afterreducing the variation in the fuel injection quantity among thecylinders in Step 105 shown in FIG. 11, when it is determined in Step151 in FIG. 13 that the valve opening characteristics of the intakevalve 2 are set so that the intake air amount to be introduced into thecylinder is limited by the valve opening characteristics of the intakevalve 2, and not limited by the cross-sectional area of the portion ofthe intake pipes 51 and 52 having the smallest internal circumference,the process proceeds to Step 153. In Step 153, the exhaust gas air-fuelratio of that cylinder is calculated and then in Step 250 and Step 251the fuel injection quantity and ignition timing, respectively, arecorrected so as to reduce the variation in torque among the cylinders.

According to the embodiment for controlling the first to the third typeof the internal combustion engine and the modifications thereof, thevariation among cylinders is controlled based on the operation angle ofthe intake valve. More specifically, when it is determined in Step 151shown in FIG. 13 whether the operation angle of the intake valve 2 isequal to or less than a predetermined threshold value, the variation inthe air-fuel ratio among the cylinders is controlled in Step 250.Therefore, when it is possible to change the operation angle of theintake valve, the variation in the air-fuel ratio among the cylinderscan be controlled more appropriately than when the variation in theair-fuel ratio among the cylinders is controlled irrespective of theaforementioned threshold value. In other words, it is possible toappropriately control the variation in the air-fuel ratio among thecylinders.

Hereinafter, additional embodiments of a control apparatus for aninternal combustion engine according to the invention will be described.The configurations of these embodiments are substantially the same asthe configurations of each of the foregoing embodiments. Also,configurations of modifications of these embodiments are substantiallythe same as the configurations of the foregoing modifications of each ofthe embodiments.

A routine according to the method for learning fuel injection quantityvariation according to the foregoing embodiments and modificationsthereof as shown in FIG. 14 is executed at predetermined intervals justas the routine shown in FIG. 11. Referring to FIG. 14, when this routinestarts, it is first determined in Step 300 whether a valve overlapamount of the intake valve 2 and the exhaust valve 3 is minimum. Whenthe determination is “NO”, i.e., when the valve overlap amount of theintake valve 2 and the exhaust valve 3 is relatively large, the intakeair amount to be introduced into the cylinder 50 is determined by thevalve overlap amount of the intake valve 2 and the exhaust valve 3. Whenthere is temporary variation in the valve overlap amount between thecylinders, a variation in the intake air amount is generated and it isdetermined that variation in the fuel injection quantity cannot belearned, and the routine ends. However, when the determination in Step300 is “YES”, the intake air amount to be introduced into the cylinder50 is determined by the opening amount of the throttle valve 56 or thecross-sectional of the portion of the intake pipes 51 and 52 having thesmallest internal circumference, because the blow back gas amount fromthe cylinder 50 to the intake pipe 51 is small. Even when there is avariation in the valve overlap amount of the intake valve 2 and theexhaust valve 3 among the cylinders, it is determined that no variationin the intake air amount is generated between the cylinders, and theprocess proceeds to Step 101.

In Step 101, it is determined whether it is time to calculate theexhaust gas air-fuel ratio of the specified cylinder, for example, thecylinder No. N, among a plurality of cylinders Nos. 1 through 4, just aswas shown in FIG. 11. When the determination is “NO”, the routine ends.When the determination is “YES”, the process proceeds to Step 102. InStep 102, the exhaust gas air-fuel ratio of the cylinder No. N, forexample, is detected for several cycles and the mean air-fuel ratiothereof is calculated, just as was shown in FIG. 11. Next in Step 103, avariation ΔQn in the fuel injection quantity among the cylindersdetected in Step 102 is calculated using the air-fuel ratio of each ofthe cylinders Nos. 1 through 4, just as was shown in FIG. 11.

Next in Step 104, a variation rate Qrate-n of the fuel injectionquantity is calculated based on the variation ΔQn in the fuel injectionquantity among the cylinders calculated in Step 103, just as was shownin FIG. 11. Then in Step 105, the fuel injection quantity of each of thecylinders Nos. 1 through 4 is corrected so as to reduce the variation inthe fuel injection quantity among the cylinders, just as was shown inFIG. 11.

According to the embodiments, when it is determined in Step 300 that thevalve overlap amount of the intake valve 2 and the exhaust valve 3 isset to the minimum value, the exhaust gas air-fuel ratio of thatcylinder is then calculated in Step 102. That is, when it is determinedin Step 300 that the valve overlap amount of the intake valve 2 and theexhaust valve 3 is set so as not to limit the intake air amount to beintroduced into the cylinder, the exhaust gas air-fuel ratio of thatcylinder is then calculated in Step 102. More specifically, when it isdetermined in Step 300 that the valve overlap amount of the intake valve2 and the exhaust valve 3 is set such that the intake air amount to beintroduced into the cylinder is limited by the opening amount of thethrottle valve 56, and not limited by the valve overlap amount, theexhaust gas air-fuel ratio of that cylinder is calculated in Step 102.In other words, for the exhaust gas air-fuel ratio of a cylinder to becalculated in Step 102, the valve overlap amount of the intake valve 2and the exhaust valve 3 is set, in a step which is not shown, such thatthe intake air amount to be introduced into that cylinder is limited bythe opening amount of the throttle valve 56, and not limited by thevalve overlap amount of the intake valve 2 and the exhaust valve 3. Thatis, by making the opening amount of the throttle valve 56 when theexhaust gas air-fuel ratio of the first cylinder No. 1 is calculated andthe opening amount of the throttle valve 56 when the exhaust gasair-fuel ratios of the other cylinders Nos. 2 through 4 are calculatedsubstantially the same, it is possible to make the intake air amount tobe introduced into the first cylinder No. 1 upon calculation of theexhaust gas air-fuel ratio thereof and the intake air amount to beintroduced into the other cylinders Nos. 2 through 4 upon calculation ofthe exhaust gas air-fuel ratios thereof the same.

Further, in the embodiments, when it is determined in Step 300 that theintake air amount to be introduced into the cylinder No. 1 when theexhaust gas air-fuel ratio thereof is calculated and the intake airamount to be introduced into the other cylinders Nos. 2 through 4 whenthe exhaust gas air-fuel ratios thereof are calculated are the same, thevariation in the fuel injection quantity among the cylinders is reducedin Step 105 based on the exhaust gas air-fuel ratio. That is, aftermaking the intake air amount in all of the cylinders the same, the fuelinjection quantity is corrected such that the exhaust gas air-fuelratios in all of the cylinders are the same. This allows both thevariation in the air-fuel ratio among cylinders, as well as thevariation in the torque among cylinders, to be reduced.

In other words, according to the embodiments, when it is determined inStep 300 that the valve opening characteristics of the intake valve 2and the exhaust valve 3 are set such that the intake air amount to beintroduced into the cylinder is limited by the opening amount of thethrottle valve 56, and not limited by the valve opening characteristicsof the intake valve 2 and the exhaust valve 3, the exhaust gas air-fuelratio of that cylinder is then calculated in Step 102. That is, for theexhaust gas air-fuel ratio of a cylinder to be calculated in Step 102,the valve opening characteristics of the intake valve 2 and the exhaustvalve 3 are set, in a step which is not shown, such that the intake airamount to be introduced into that cylinder is limited by the openingamount of the throttle valve 56, and not limited by the valve openingcharacteristics of the intake valve 2 and the exhaust valve 3.

Also, according to modifications of the embodiments in which thethrottle valve 56 is not provided, just as in the embodiments, when itis determined in Step 300 that the valve overlap amount of the intakevalve 2 and the exhaust valve 3 is set to the minimum value, the exhaustgas air-fuel ratio of that cylinder is calculated in Step 102. That is,when it is determined in Step 300 that the valve overlap amount of theintake valve 2 and the exhaust valve 3 is set so as not to limit theintake air amount to be introduced into the cylinder, the exhaust gasair-fuel ratio of that cylinder is then calculated in Step 102. Morespecifically, when it is determined in Step 300 that the valve overlapamount of the intake valve 2 and the exhaust valve 3 is set such thatthe intake air amount to be introduced into the cylinder is limited bythe cross-sectional area of a portion of the intake pipes 51 and 52having the smallest internal circumference, and not limited by the valveoverlap amount of the intake valve 2 and the exhaust valve 3, theexhaust gas air-fuel ratio of that cylinder is then calculated in Step102. In other words, for the exhaust gas air-fuel ratio of a cylinder tobe calculated in Step 102, the valve overlap amount of the intake valve2 and the exhaust valve 3 are set, in a step which is not shown, to theminimum value such that the intake air amount to be introduced into thecylinder is limited by the cross-sectional area of a portion of theintake pipes 51 and 52 having the smallest internal circumference, andnot limited by the valve overlap amount of the intake valve 2 and theexhaust valve 3.

In other words, according to modifications of the embodiments, when itis determined in Step 300 that the valve opening characteristics of theintake valve 2 and the exhaust valve 3 are set such that the intake airamount to be introduced into the cylinder is limited by thecross-sectional area of a portion of the intake pipes 51 and 52 havingthe smallest internal circumference, and not limited by the valveopening characteristics of the intake valve 2 and the exhaust valve 3,the exhaust gas air-fuel ratio of that cylinder is then calculated inStep 102. That is, for the exhaust gas air-fuel ratio of a cylinder tobe calculated in Step 102, the valve opening characteristics of theintake valve 2 and the exhaust valve 3 are set, in a step which is notshown, such that the intake air amount to be introduced into thatcylinder is limited by the cross-sectional area of a portion of theintake pipes 51 and 52 having the smallest internal circumference, andnot limited by the valve opening characteristics of the intake valve 2and the exhaust valve 3.

Also, according to the foregoing embodiments and modifications, thevariation among cylinders is able to be reduced based on the valveoverlap amount of the intake valve 2 and the exhaust valve 3. Morespecifically, the variation in the fuel injection quantity amongcylinders can be reduced based on the valve overlap amount of the intakevalve 2 and the exhaust valve 3. Even more specifically, when it isdetermined in Step 300 in FIG. 14 that the valve overlap amount of theintake valve 2 and the exhaust valve 3 is set to the minimum value, thevariation in the fuel injection quantity among the cylinders is reducedin Step 105. Therefore, when it is possible to change the valve overlapamount of the intake valve and the exhaust valve, the variation in theair-fuel ratio among the cylinders can be controlled more appropriatelythan when the variation among cylinders is not reduced based on thevalve overlap amount of the intake valve and the exhaust valve. In otherwords, it is possible to appropriately control the variation in theair-fuel ratio among the cylinders.

A routine according to the method for learning valve overlap amountvariation, according to another embodiment and a modification thereof,in FIG. 15 is executed at predetermined intervals, just as the routineshown in FIG. 14. Referring to FIG. 15, when this routine starts, it isfirst determined in Step 150 whether the control in Step 105 in FIG. 14has been completed. If the correction of the fuel injection quantity forall of the cylinders is not yet complete, it is determined that thevariation in the valve overlap amount of the intake valve 2 and theexhaust valve 3 among the cylinders can not be reduced and the routineends. If the correction of the fuel injection quantity for all of thecylinders is complete, then the process proceeds to Step 450. In Step450, it is determined whether the valve overlap amount of the intakevalve 2 and the exhaust valve 3 is equal to or greater than apredetermined threshold value. That is, it is determined whether thevalve overlap amount of the intake valve 2 and the exhaust valve 3 isset to a relatively large value such that the intake air amount to beintroduced into the cylinder is limited by the valve overlap amount ofthe intake valve 2 and the exhaust valve 3, and not limited by theopening amount of the throttle valve 56. If the determination in step450 is “NO”, the routine ends. If the determination is “YES”, theprocess proceeds to Step 152.

In Step 152, it is determined whether it is time to calculate theexhaust gas air-fuel ratio of the specified cylinder, for example, thecylinder No. N, among a plurality of cylinders Nos. 1 through 4, just aswas shown in FIG. 12. If the determination is “NO”, the routine ends. Ifthe determination is “YES”, the process proceeds to Step 153. In Step153, the exhaust gas air-fuel ratio of the cylinder No. N, for example,is detected for several cycles and the mean air-fuel ratio thereof iscalculated, just as in FIG. 12. Next, in Step 154, the variation ΔQ inthe intake air amount among the cylinders is calculated using theair-fuel ratio of each of the cylinders Nos. 1 through 4 calculated inStep 153 on the assumption that the fuel injection quantities of all ofthe cylinders Nos. 1 through 4 are the same.

Next in Step 451, a variation ΔVo in the valve overlap amount of theintake valve 2 and the exhaust valve 3 of the specified cylinder, forexample, cylinder No. N, is calculated based on the variation ΔQ in theintake air amount among the cylinders calculated in Step 154. Thiscalculation of the variation ΔVo in the valve overlap amounts of theintake valves 2 and the exhaust valves 3 is performed for all of thecylinders Nos. 1 through 4. Next in Step 452, the intake valve drivingdevice 58 corrects the opening timing of the intake valves 2 of each ofthe cylinders Nos. 1 through 4, while the intake valve driving device58′ corrects the closing timing of the exhaust valves 3 of each of thecylinders Nos. 1 through 4, such that the variation in the valve overlapamounts of the intake valves 2 and exhaust valves 3 among the cylindersis reduced, i.e., such that the variation in the intake air amount amongthe cylinders is reduced.

According to the embodiment, after reducing the variation in the fuelinjection quantity among the cylinders in Step 105 in FIG. 14, when itis determined in Step 450 in FIG. 15 that the valve openingcharacteristics of the intake valve 2 and the exhaust valve 3 are set sothat the intake air amount to be introduced into the cylinder is limitedby the valve opening characteristics of the intake valve 2 and theexhaust valve 3, and not limited by the opening amount of the throttlevalve 56, the process proceeds to Step 153. In Step 153, the exhaust gasair-fuel ratio of that cylinder is calculated and then in Step 452, thevariation in the valve opening characteristics of the intake valve 2 andthe exhaust valve 3 among cylinders is reduced based on that exhaust gasair-fuel ratio. That is, after reducing the variation in the fuelinjection quantity among the cylinders, the valve openingcharacteristics of the intake valves 2 and exhaust valves 3 of each ofthe cylinders Nos. 1 through 4 are changed such that the exhaust gasair-fuel ratio of the cylinder No. 1 and the exhaust gas air-fuel ratiosof the other cylinders Nos. 2 through 4 are the same. Therefore, even ifthere is variation in the fuel intake quantity among cylinders, novariation in torque among cylinders is generated and the variation inthe valve opening characteristics of the intake valves 2 and exhaustvalves among the cylinders can be reduced.

Also according to a modification of the embodiment, after reducing thevariation in the fuel injection quantity among the cylinders in Step 105in FIG. 14, when it is determined in Step 450 in FIG. 15 that the valveopening characteristics of the intake valve 2 and the exhaust valve 3are set so that the intake air amount to be introduced into the cylinderis limited by the valve opening characteristics of the intake valve 2and the exhaust valve 3, and not limited by the cross-sectional area ofthe portion of the intake pipes 51 and 52 having the smallest internalcircumference, the process proceeds to Step 153. In Step 153, theexhaust gas air-fuel ratio of that cylinder is calculated and then inStep 452, the variation in the valve opening characteristics of theintake valve 2 and exhaust valve 3 among cylinders is reduced based onthat exhaust gas air-fuel ratio. That is, after reducing the variationin the fuel injection quantity among the cylinders, the valve openingcharacteristics of the intake valves 2 and exhaust valves 3 of each ofthe cylinders Nos. 1 through 4 are changed such that the exhaust gasair-fuel ratio of the cylinder No. 1 and the exhaust gas air-fuel ratiosof the other cylinders Nos. 2 through 4 are the same. Therefore, even ifthere is variation in the fuel intake quantity among cylinders, novariation in torque among cylinders is generated and the variation inthe valve opening characteristics of the intake valves 2 and exhaustvalves 3 among the cylinders can be reduced.

More specifically, according to the embodiment and the modificationthereof, after reducing the variation in the fuel injection quantityamong the cylinders in Step 105 in FIG. 14, when it is determined inStep 450 in FIG. 15 that the valve overlap amount of the intake valve 2and the exhaust valve 3 is set to the minimum value, the processproceeds to Step 153. In Step 153, the exhaust gas air-fuel ratio iscalculated and then in Step 451, the variation in the valve overlapamount of the intake valve 2 and the exhaust valve 3 among cylinders isreduced based on that exhaust gas air-fuel ratio. That is, afterreducing the variation in the fuel injection quantity among thecylinders, the valve overlap amount of the intake valve 2 and theexhaust valve 3 of each of the cylinders Nos. 1 through 4 is changedsuch that the exhaust gas air-fuel ratio of the cylinder No. 1 and theexhaust gas air-fuel ratios of the other cylinders Nos. 2 through 4 arethe same. Therefore, even if there is variation in the fuel intakequantity among cylinders, no variation in torque among cylinders isgenerated and the variation in the valve overlap amount of the intakevalve 2 and the exhaust valve 3 among the cylinders can be reduced.

In other words, according to the embodiment and the modificationthereof, after reducing the variation in the fuel injection quantityamong the cylinders in Step 105 in FIG. 14, when it is determined inStep 450 in FIG. 15 that the valve overlap amount of the intake valve 2and the exhaust valve 3 is set to a predetermined valve overlap amountthat is larger than the minimum valve overlap amount, the processproceeds to Step 153. In Step 153, the exhaust gas air-fuel ratio iscalculated and then in Step 452 the variation in the intake air amountamong cylinders is reduced with that exhaust gas air-fuel ratio. Thatis, after reducing the variation in the fuel injection quantity amongthe cylinders, the valve overlap amount of the intake valve 2 and theexhaust valve 3 of each of the cylinders Nos. 1 through 4 is changedsuch that the exhaust gas air-fuel ratio of the cylinder No. 1 and theexhaust gas air-fuel ratios of the other cylinders Nos. 2 through 4 arethe same. Therefore, even if there is variation in the fuel intakequantity between cylinders, no variation in torque between cylinders isgenerated and the variation in the intake air amount between thecylinders can be reduced.

Also according to the embodiment and the modification thereof avariation among cylinders is reduced by the valve overlap amount of theintake valve and the exhaust valve. More specifically, when it isdetermined in Step 450 in FIG. 15 that the valve overlap amount of theintake valve 2 and the exhaust valve 3 is equal to, or greater than, apredetermined threshold value, the variation in the valve overlap amountof the intake valve 2 and the exhaust valve 3 among the cylinders isreduced in Step 452. Therefore, when it is possible to change the valveoverlap amount of the intake valve and the exhaust valve, it is possibleto control the variation in the air-fuel ratio between the cylindersmore appropriately than when the variation in the valve overlap amountof the intake valve 2 and the exhaust valve 3 between the cylinders iscontrolled irregardless of the aforementioned threshold value. In otherwords, it is possible to appropriately control the variation in theair-fuel ratio among the cylinders.

A routine according to the method for learning intake valve operationangle variation, according to the foregoing embodiments andmodifications thereof, in FIG. 16 is performed at predeterminedintervals, just as the routine shown in FIG. 14. As shown in FIG. 16,when this routine starts, it is first determined in Step 150 whether thecorrection control in Step 105 in FIG. 14 has been completed, just as inFIG. 15. If the correction is not yet complete, it is determined thatthe variation in the valve overlap amount of the intake valve 2 and theexhaust valve 3 among the cylinders can not be reduced and the routineends. If the correction of the fuel injection quantity for all of thecylinders is complete, then the process proceeds to Step 450. In Step450, it is determined whether the valve overlap amount of the intakevalve 2 and exhaust valve 3 is equal to or greater than a predeterminedthreshold value, just as in FIG. 15. If the determination is “NO”, theroutine ends. If the determination is “YES”, the process proceeds toStep 152.

In Step 152, it is determined whether it is time to calculate theexhaust gas air-fuel ratio of a specified cylinder, for example, thecylinder No. N, among a plurality of cylinders Nos. 1 through 4, just asin FIG. 15. If the determination is “NO”, the routine ends. If thedetermination is “YES”, the process proceeds to Step 153. In Step 153,the exhaust gas air-fuel ratio of the cylinder No. 1, for example, isdetected for several cycles and the mean air-fuel ratio thereof iscalculated, just as in FIG. 15. Next in Step 154, the variation ΔQ inthe intake air amount among the cylinders is calculated using theair-fuel ratio of each of the cylinders Nos. 1 through 4 calculated inStep 153 on the assumption that the fuel injection quantity in each ofthe cylinders Nos. 1 through 4 are the same, just as in FIG. 15.

Next in Step 250, the fuel injection quantity of each cylinder iscorrected based on the variation ΔQ in the intake air amount among thecylinders calculated in Step 154 such that the torque of all of thecylinders Nos. 1 through 4 is the same, just as in FIG. 13. Then in Step251, just as in FIG. 13, the ignition timing of each cylinder iscorrected based on the variation ΔQ in the intake air amount among thecylinders calculated in Step 154 such that the torque of all of thecylinders Nos. 1 through 4 is the same. For example, the ignition timingin a cylinder in which the intake air amount is relatively large isretarded during operation under high load of the engine, which tends tocause knocking.

According to the foregoing embodiments, after reducing the variation inthe fuel injection quantity among the cylinders in Step 105 in FIG. 14,when it is determined in Step 450 in FIG. 16 that the valve openingcharacteristics of the intake valve 2 and the exhaust valve 3 are set sothat the intake air amount to be introduced into the cylinder is limitedby the valve opening characteristics of the intake valve 2 and theexhaust valve 3, and not limited by the opening amount of the throttlevalve 56, the process proceeds to Step 153. In Step 153, the exhaust gasair-fuel ratio of that cylinder is calculated and then in Step 250 andStep 251, the fuel injection quantity and ignition timing, respectively,are corrected so as to reduce the variation in torque among thecylinders.

Also according to the foregoing embodiments and modifications thereof,after reducing the variation in the fuel injection quantity among thecylinders in Step 105 in FIG. 14, when it is determined in Step 450 inFIG. 16 that the valve opening characteristics of the intake valve 2 andthe exhaust valve 3 are set so that the intake air amount to beintroduced into the cylinder is limited by the valve openingcharacteristics of the intake valve 2 and the exhaust valve 3, and notlimited by the cross-sectional area of the portion of the intake pipes51 and 52 having the smallest internal circumference, the processproceeds to Step 153. In Step 153, the exhaust gas air-fuel ratio ofthat cylinder is calculated and then in Step 250 and Step 251, the fuelinjection quantity and ignition timing, respectively, are corrected soas to reduce the variation in torque among cylinders.

Also according to the foregoing embodiments and modifications thereof,the variation among cylinders is controlled by the valve overlap amountof the intake valve and the exhaust valve. More specifically, when it isdetermined in Step 450 in FIG. 16 that the valve overlap amount of theintake valve 2 and the exhaust valve 3 is equal to or greater than apredetermined threshold value, the variation in the air-fuel ratio amongthe cylinders is reduced in Step 250. Therefore, when it is possible tochange the valve overlap amount of the intake valve and the exhaustvalve, the variation in the air-fuel ratio among the cylinders can becontrolled more appropriately than when the variation in the air-fuelratio among the cylinders is controlled irrespective of theaforementioned threshold. In other words, it is possible toappropriately control the variation in the air-fuel ratio among thecylinders.

Hereinafter, an another embodiment of a control apparatus for aninternal combustion engine according to the invention will be described.The configuration of this embodiment is a combination of theconfiguration of the foregoing embodiments and modifications thereof andthe configuration described below. In FIG. 17, reference numerals thatare the same as those in FIGS. 1 through 10 represent the same or likeparts as those shown in FIGS. 1 through 10. FIG. 17 also shows an intakeair amount calculating portion 22′ which constitutes a portion of theECU 22, a neural network 60 which is of a construction substantially thesame as that of the well-known neural network disclosed in JapanesePatent Application Laid-Open Publication No. 9-88685, for example, and adelay calculating portion 22″ using the neural network 60, whichconstitutes another portion of the ECU 22.

In this embodiment, the variation among the cylinders is reduced usingthe neural network 60 in order to compensate for the delay from thevalve lift amount changing device 9, 9′, the opening/closing timingshift device 11, 11′, the intake valve driving device 58, and theexhaust valve driving device 58′ during times of excessive driving ofthe engine. Specifically, when the intake air amount is calculatedduring times of excessive driving of the engine, the intake air amountis estimated based on the value output from the airflow meter 19, theopening amount of the throttle valve 56, the rate of change of thethrottle valve opening amount, the valve opening timing of the intakevalve 2, the valve closing timing of the intake valve 2, the enginespeed, the water temperature, the oil temperature, the oil pressure, andthe value output from the intake air temperature sensor 21. The neuralnetwork 60 is able to learn the delay from the difference between thatintake air amount and an air amount calculated based on the value outputfrom the air-fuel ratio sensor 57. As a result, the actual air-fuelratio can be matched extremely accurately to the target air-fuel ratiounder any condition.

That is, the neural network is applied for the calculating portion thatcalculates the intake air amount delay, and the intake air amount iscalculated based on the above-described data. The error, or difference,between the fuel injection quantity calculated based on that intake airamount and the actual exhaust gas air-fuel ratio of that cycle is thendetected. By repeating this with various patterns and correcting thesensitivity coefficient of each parameter, the actual air-fuel ratio isable to be matched extremely accurately to the target air-fuel ratiounder any operating condition of the engine.

Hereinafter, another embodiment of a control apparatus for an internalcombustion engine according to the invention will be described. Theconfiguration of this embodiment is substantially the same as any of theconfigurations of the foregoing embodiments and modifications thereof.Alternatively, the eighth embodiment may also comprise a plurality ofintake valve cams with different cam profiles, not shown, wherein thevalve opening characteristics of each intake valve is able to be changedby changing the intake valve cam.

A routine according to the method for controlling to minimize variationbetween cylinders according to the foregoing embodiment and themodification thereof, is performed at predetermined intervals. As shownin FIG. 18, when this routine starts, it is first determined in Step 500whether a map, to be described later, has already been created. If thedetermination is “YES”, the process proceeds to Step 505. If thedetermination is “NO”, the process proceeds to Step 501. In Step 501,the air-fuel ratio of each of the cylinders Nos. 1 through 4 in aconstant state, such as when the engine is idling, is calculated basedon a value output from the air-fuel ratio sensor 57 by a method such asthat disclosed in Japanese Patent Application Laid-Open Publication No.59-101562 or Japanese Patent Application Laid-Open Publication No.5-180040.

Next in Step 502, it is determined whether there is variation in theair-fuel ratio among the cylinders. When variation in the air-fuel ratiobetween the cylinders is less than a predetermined value, the routineends. When variation in the air-fuel ratio among the cylinders is equalto or greater than the predetermined value, the process proceeds to Step503. In Step 503, fuel injection amount correction coefficients for eachof the cylinders Nos. 1 through 4 are calculated based on the calculatedair-fuel ratios of each of the cylinders Nos. 1 through 4, respectively.For example, when the actual air-fuel ratio of a cylinder varies on therich side with respect to the target air-fuel ratio, a fuel injectionamount correction coefficient is calculated which has a relatively smallvalue so as to correct with a decrease the fuel injection amount of thatcylinder. On the other hand, when the actual air-fuel ratio of acylinder varies on the lean side with respect to the target air-fuelratio, a fuel injection amount correction coefficient is calculatedwhich has a relatively large value so as to correct with an increase thefuel injection amount of that cylinder.

Next in Step 504, a fuel injection quantity correction coefficient map,which shows the relationship between the fuel injection quantitycorrection coefficient and the operation angle of the intake valve 2, iscreated based on the fuel injection amount quantity correctioncoefficient calculated in Step 503 and the operation angle of the intakevalve 2 at that time. As shown in FIG. 19, when a point P1 is calculatedin Step 503, a curved line L1 showing the relationship between the fuelinjection quantity correction coefficient and the operation angle of theintake valve is calculated from that point P1, and a fuel injectionquantity correction coefficient map is created based on that curved lineL1. According to a modification of the eighth embodiment, in Step 504 itis possible to calculate a relational expression that simplifies thecurved line L1 instead of creating the map. Also according to amodification of the embodiment, it is possible to calculate not only thepoint P1 but also a point P1′ in a step similar to Step 503, calculate acurved line similar to the curved line L1 based on the point P1 and thepoint P1′, and then create a fuel injection quantity correctioncoefficient map based on that curved line.

In Step 505, the fuel injection quantity for each of the cylinders Nos.1 through 4 is corrected. That is, when the map shown in FIG. 19 has notbeen created such that the determination in Step 500 is “NO”, a fuelinjection quantity correction coefficient for correcting the fuelinjection quantity is calculated in Step 503, and the fuel injectionquantity is then corrected based on that fuel injection quantitycorrection coefficient in Step 505. On the other hand, when the mapshown in FIG. 19 has already been created such that the determination inStep 500 is “YES”, Step 503 is not performed even when the operationangle of the intake valve 2 has changed from the point at which the mapwas created, such that the fuel injection quantity is corrected in Step505 based on the map that was already created.

When it is feared that hunting may occur when the aforementioned Step505 is performed, the fuel injection quantity correction coefficientsmay be smoothed out in a step which is not shown, so that it is thenpossible to correct the fuel injection quantity in a step which replacesStep 505 based on the smoothed out fuel injection quantity correctioncoefficient. (In this case, the fuel injection quantity correctioncoefficients of all of the cylinders are corrected using the values ofthe smoothed out fuel injection quantity correction coefficients. Thethus corrected fuel injection quantity correction coefficients are thenrepeatedly smoothed and re-corrected until they converge on a singlefuel injection quantity correction coefficient for all of the cylinders.The fuel injection quantity is then corrected based on this single fuelinjection quantity correction coefficient.)

According to the embodiment or the modification thereof, a variationbetween cylinders is reduced by the operation angle of the intake valve2. More specifically, as shown in FIG. 19, the variation in the fuelinjection quantity among cylinders is reduced by calculating the fuelinjection quantity correction coefficient of each cylinder No. 1 through4based on the operation angle of the intake valve 2, and correcting thefuel injection quantity in each cylinder No. 1 through 4 in Step 505based on that fuel injection quantity correction coefficient. Therefore,when it is possible to change the operation angle of the intake valve,it is possible to control the variation in the air-fuel ratio among thecylinders more appropriately than when the variation between cylindersis not controlled by the operation angle of the intake valve.

Also according to the embodiment or the modification thereof, becausethe variation among the cylinders is controlled by the operation angleof the intake valve, it is possible to appropriately control thevariation between the cylinders even when, for example, the sensor 57 isnot sufficiently exposed to the exhaust gas such that a target air-fuelratio calculated from a value output by a sensor is not an appropriatetarget air-fuel ratio.

Also, according to the embodiment or the modification thereof, thevariation in the air-fuel ratio among the cylinders is reduced bycorrecting the fuel injection quantity in Step 505 based on theoperation angle of the intake valve 2. For example, when the air-fuelratio of a cylinder varies to the rich side, the variation in theair-fuel ratio among the cylinders is reduced by correcting with adecrease the fuel injection quantity of that cylinder. Also, the smallerthe operation angle of the intake valve, the greater the variation inthe air-fuel ratio among cylinders when the actual operation angle isoff from the target operation angle. In view of this, as shown in FIG.19, the difference between the fuel injection quantity correctioncoefficient and 1.0 is made to become larger as the operation angle ofthe intake valve becomes smaller. As a result, the variation in theair-fuel ratio among the cylinders is controlled by increasing thecorrection amount of the fuel injection quantity. This enables thevariation in the air-fuel ratio among cylinders to be controlled moreappropriately than when the fuel injection quantity is not corrected bythe operation angle of the intake valve.

More specifically, when a variation in the air-fuel ratio among thecylinders is detected in Step 501 and Step 502, the fuel injectionquantity correction coefficient for decreasing that variation iscalculated in Step 503. Then in Step 504, a relationship L1 between thefuel injection quantity correction coefficient and the operation angleof the intake valve is calculated based on that fuel injection quantitycorrection coefficient and the operation angle of the intake valve atthat time. When the operation angle of the intake valve changes, thefuel injection quantity correction coefficient after the intake valveoperation angle change is calculated based on the operation angle of theintake valve after the change and that relationship L1.

Hereinafter an another embodiment of a control apparatus for an internalcombustion engine according to the invention will be described. Theconfiguration of this embodiment is substantially the same as that ofthe eighth embodiment described above.

A routine according to the method for controlling to correct a targetair-fuel ratio, according to the embodiment, is performed atpredetermined intervals. As shown in FIG. 20, when this routine starts,it is first determined in Step 600 whether a map, to be described later,has already been created. If the determination is “YES”, the processproceeds to Step 604. If the determination is “NO”, the process proceedsto Step 501. In Step 501, the air-fuel ratio of each of the cylindersNos. 1 through 4 in a constant state, such as when the engine is idling,is calculated based on a value output from the air-fuel ratio sensor 57,just as in the previous embodiment.

Next in Step 502, it is determined whether there is variation in theair-fuel ratio among the cylinders, just as in the previous embodiment.When the variation in the air-fuel ratio among the cylinders is less apredetermined value, the routine ends. When variation in the air-fuelratio between the cylinders is equal to or greater than thepredetermined value, the process proceeds to Step 601. In Step 601, amean air-fuel ratio injection amount is calculated for all of thecylinders Nos. 1 through 4. The mean air-fuel ratio injection amount forall of the cylinders Nos. 1 through 4 is calculated, for example, byadding up the air-fuel ratios for each of the cylinders Nos. 1 through 4and dividing the sum by 4. Next in Step 602, a new target air-fuel ratio(hereinafter referred to as “corrected target air-fuel ratio”) iscalculated based on the target air-fuel ratio which is based on thevalue output from the sensor 57 (hereinafter referred to as “sensortarget air-fuel ratio”) and, for example, a stoichiometric air-fuelratio, and the mean air-fuel ratio calculated in Step 601. That is, thesensor target air-fuel ratio is corrected and the corrected targetair-fuel ratio is calculated.Corrected target air-fuel ratio=Sensor target air-fuelratio×Stoichiometric air-fuel ratio/Mean air-fuel ratio  (1)

When there is a fear of hunting from Expression (1) above, or when theaccuracy of the mean air-fuel ratio calculated in Step 601 is low, thesmoothed out corrected target air-fuel ratio can also be calculated, asshown in Expression (2). (In this case, the air-fuel ratios of all ofthe cylinders are calculated using the values of the smoothed outcorrected target air-fuel ratios. The thus corrected target air-fuelratios of all of the cylinders are then repeatedly smoothed andre-corrected until they converge on a single corrected target air-fuelratio for all of the cylinders. A target air-fuel ratio map is thencreated in Step 603 using this single corrected target air-fuel ratio.Corrected target air-fuel ratio=(Stoichiometric air-fuel ratio−meanair-fuel ratio)/k+sensor target air-fuel ratio  (2);wherein k is a positive integer.

Next in Step 603, the target air-fuel ratio map showing the relationshipbetween the corrected target air-fuel ratio and the operation angle ofthe intake valve 2 is created based on the corrected target air-fuelratio calculated in Step 602 and the operation angle of the intake valve2 at that time. As shown in FIG. 21, when a point P2 is calculated inStep 602, a curved line L2 showing the relationship between thecorrected target air-fuel ratio and the operation angle of the intakevalve is calculated from that point P2. The target air-fuel ratio map isthen created based on that curved line L2. According to a modificationof the ninth embodiment of the invention, in Step 603 it is possible tocalculate a relational expression that simplifies the curved line L2instead of creating the map. Also according to another modification ofthe embodiment, it is possible to calculate not only the point P2 butalso a point P2′ in a step similar to Step 602, calculate a curved linesimilar to the curved line L2 based on the point P2 and the point P2′,and then create a fuel injection quantity correction coefficient mapbased on that curved line.

In Step 604, feedback control for the air-fuel ratio is performed. Thatis, a fuel injection quantity for all of the cylinders Nos. 1 through 4is uniformly corrected based on the corrected target air-fuel ratio onthe map created in Step 603. In other words, when the map shown in FIG.21 has not been created such that the determination in Step 600 is “NO”,the corrected target air-fuel ratio for performing feedback control forthe air-fuel ratio is calculated in Step 602 and feedback control forthe air-fuel ratio is performed in Step 604 based on the that correctedtarget air-fuel ratio. On the other hand, when the map shown in FIG. 21has already been created such that the determination in Step 600 is“YES”, Step 602 is not performed even when the operation angle of theintake valve 2 has changed from the point at which the map was created,such that the feedback control for the air-fuel ratio is performed inStep 604 based on the map that was already created.

According to the embodiment of the invention, the fuel injectionquantity is calculated based on the following Equations (3) and (4).Fuel injection quantity=Basic injection quantity+Feedback correctionquantity  (3)Feedback correction quantity=a×f+b×g  (4);wherein a and b denote gain, and f and g denote coefficients of thecorrected target air-fuel ratio and the sensor target air-fuel ratio.

That is, when the corrected target air-fuel ratio shifts over to thelean side, for example, the feedback correction quantity is reduced suchthat the fuel injection quantity is corrected with a reduction. On theother hand, when the corrected target air-fuel ratio shifts over to therich side, for example, the feedback correction quantity is increasedsuch that the fuel injection quantity is corrected with an increase.

According to this embodiment of the invention, therefore, the targetair-fuel ratio is corrected based on the operation angle of the intakevalve 2, i.e., the corrected target air-fuel ratio is changed based onthe operation angle of the intake valve 2. Alternatively, according to amodification of the embodiment (refer to FIG. 21), any one, or all, ofthe coefficients relating to the air-fuel ratio feedback control may becorrected by the operation angle of the intake valve 2. Thesecoefficients include the aforementioned corrected target air-fuel ratio,as well as the gain a and b, and the sensor target air-fuel ratio andthe like.

Alternatively, according to another modification of the ninth embodimentof the invention, the fuel injection quantity is calculated based on thefollowing Equations (5) and (6).Fuel injection quantity=Basic injection quantity+Increase correctionquantity+Feedback correction quantity  (5)Feedback correction quantity=A×P+ΣA×I+(dA/dt)×D  (6);wherein A denotes the difference between the corrected target air-fuelratio and the sensor target air-fuel ratio, and P, I and D denote thegain increase correction quantity which includes a correction quantityfor minimizing an increase in exhaust temperature and a correctionquantity when the engine coolant temperature is low.

According to a modification of the embodiment, it is possible to correctany one, or all, of the coefficients relating to air-fuel ratio feedbackcontrol by the operation angle of the intake valve 2. These coefficientsinclude the aforementioned corrected target air-fuel ratio, as well asthe gains P, I and D, and the difference A between the corrected targetair-fuel ratio and the sensor target air-fuel ratio and the like.

According to the embodiment or the modification thereof, a predeterminedcoefficient relating to the air-fuel ratio feedback control is correctedby the operation angle of the intake valve 2. More specifically, thetarget air-fuel ratio is calculated based on the operation angle of theintake valve 2, as shown in FIG. 21. For example, in the event that theoverall air-fuel ratio shifts over to the rich side as a result of thesensor target air-fuel ratio not being set appropriately due to the factthat the sensor 57 is not sufficiently exposed to the gas, the correctedtarget air-fuel ratio is calculated so as to shift the overall air-fuelratio toward the lean side.

Also according to the ninth embodiment or a modification thereof, whenthe actual operation angle of the intake valve 2 is off from the targetoperation angle thereof, there is a tendency for the sensor targetair-fuel ratio, which is set based on a value output by the sensor 57,to be far off from the appropriate target air-fuel ratio the smaller theoperation angle of the intake valve 2. In view of this fact, as is shownin FIG. 21, for example, the correction amount for the target air-fuelratio increases, i.e., the difference between the corrected targetair-fuel ratio and the stoichiometric air-fuel ratio increases, thesmaller the operation angle of the intake valve 2. This enables thevalue of the target air-fuel ratio to be made more appropriate than whenthe target air-fuel ratio is not corrected based on the operation angleof the intake valve 2. That is, the control apparatus is capable ofexecuting appropriate air-fuel ratio feedback control even when thesensor 57 is not sufficiently exposed to the exhaust gas, i.e., evenwhen the sensor target air-fuel ratio calculated from a value output bythe sensor 57 is not an appropriate target air-fuel ratio.

More specifically, when a variation in the air-fuel ratio betweencylinders is detected in Steps 501 and 502, the control apparatus firstcalculates a target air-fuel ratio (corrects it to an appropriate targetair-fuel ratio) in Step 602, and then calculates the relationship L2between the target air-fuel ratio and the operation angle of an intakevalve based on that target air-fuel ratio and the operation angle of theintake valve at that time in Step 603. The control apparatus thencalculates, when the operation angle of the intake valve changes, theappropriate target air-fuel ratio after the intake valve operation anglechange based on the operation angle of the intake valve 2 after thechange and that relationship L2.

Hereinafter an another embodiment of a control apparatus for an internalcombustion engine according to the invention will be described. Theconfiguration of this embodiment is substantially the same as those ofthe aforementioned embodiments. Accordingly, this embodiment hassubstantially the same effects and advantages as those embodiments.

A routine according to a method for controlling to reduce variationamong cylinders, according to the embodiment, is performed atpredetermined intervals. As shown in FIG. 22, when this routine starts,the air-fuel ratio of each of the cylinders Nos. 1 through 4when theengine is in a constant state such as idling, for example, is firstcalculated in Step 501 based on the value output from the air-fuel ratiosensor 57, just as in the foregoing embodiments. Then in Step 502 it isdetermined whether there is a variation in the air-fuel ratio betweenthe cylinders, just as in the other embodiments. If the determination is“YES”, the process proceeds to Step 503. If the variation in theair-fuel ratio between the cylinders is less than a predetermined value,then the routine ends. If the variation in the air-fuel ratio betweencylinders is equal to or greater than the predetermined value, then theroutine proceeds to Step 503.

In Step 503, the fuel injection quantity correction coefficient for eachof the cylinders Nos. 1 through 4 is calculated based on the calculatedair-fuel ratios of each of the cylinders Nos. 1 through 4, respectively,just as in the former embodiments. For example, when the actual air-fuelratio varies on the rich side with respect to the target air-fuel ratio,a fuel injection amount correction coefficient is calculated which has arelatively small value so as to correct with a decrease the fuelinjection amount. On the other hand, when the actual air-fuel ratiovaries on the lean side with respect to the target air-fuel ratio, afuel injection amount correction coefficient is calculated which has arelatively large value so as to correct with an increase the fuelinjection amount. Next in Step 700, it is determined whether the fuelinjection quantity correction coefficient calculated in Step 503 iswithin a predetermined value range. When the fuel injection quantitycorrection coefficient is too small, the process proceeds to Step 701.The routine also proceeds to Step 701 when the fuel injection quantitycorrection coefficient is too large. On the other hand, when the fuelinjection quantity correction coefficient falls within the predeterminedvalue range, the process proceeds to Step 500.

In Step 500, it is determined whether a fuel injection quantitycorrection coefficient map has already been created. When thedetermination is “NO”, the process proceeds to Step 504. When thedetermination is “YES”, the process proceeds to Step 505. In Step 504, afuel injection quantity correction coefficient map, which shows therelationship between the fuel injection quantity correction coefficientand the operation angle of the intake valve 2, as shown in FIG. 19, iscreated based on the fuel injection amount quantity correctioncoefficient calculated in Step 503 and the operation angle of the intakevalve 2 at that time, just as in the former embodiments. In Step 505,the fuel injection quantity for each of the cylinders Nos. 1 through 4is corrected. In other words, when the map shown in FIG. 19 has not beencreated such that the determination in Step 500 is “NO”, the fuelinjection quantity is corrected based on the fuel injection quantitycorrection coefficient calculated in Step 503. On the other hand, whenthe map shown in FIG. 19 has already been created such that thedetermination in Step 500 is “YES”, the fuel injection quantity iscorrected based on the map that was already created.

In Step 701, the fuel injection quantity correction coefficientcalculated in Step 503 is guarded by a predetermined upper limit andlower limit. Then in Step 600 it is determined whether a target air-fuelratio map has already been created, just as in the former embodiments.If the determination is “YES”, the process proceeds to Step 604. If thedetermination is “NO”, then the process proceeds to Step 601. In Step601, a mean air-fuel ratio for all of the cylinders Nos. 1 through 4 iscalculated, just as in the former embodiments. Then in Step 602, acorrected target air-fuel ratio is calculated based on the sensor targetair-fuel ratio and, for example, the stoichiometric air-fuel ratio, andthe mean air-fuel ratio calculated in Step 601, just as in the formerembodiment. Next, in Step 603, a target air-fuel ratio map, which showsthe relationship of the corrected target air-fuel ratio and theoperation angle of the intake valve 2, is created based on the correctedtarget air-fuel ratio calculated in Step 602 and the operation angle ofthe intake valve 2 at that time, just as in the ninth embodiment.

In Step 604, air-fuel ratio feedback control is performed, just as inthe ninth embodiment. Because the fuel injection quantity correctioncoefficient is guarded in Step 701, as described above, the correctionamount of the fuel injection quantity will not become very large.

According to the aforementioned embodiment, the target air-fuel ratio iscorrected by the operation angle of the intake valve 2, i.e., thecorrected target air-fuel ratio is changed by the operation angle of theintake valve 2. Alternatively, according to a modification of theembodiment (refer to FIG. 21), any one, or all, of the coefficientsrelating to the air-fuel ratio feedback control may be corrected by theoperation angle of the intake valve 2, just as in the modification ofthe ninth embodiment.

Also, according to another modification of the embodiment, the fuelinjection quantity is calculated based on the foregoing Expressions (5)and (6), just as in the other modification of the embodiment. Moreoveraccording to a modification of the embodiment, any one, or all, of thecoefficients relating to the air-fuel ratio feedback control can becalculated based on the operation angle of the intake valve 2, just asin the modification of the ninth embodiment.

The embodiment has substantially the same effects and advantages as theeighth and ninth embodiments. Moreover, according to the embodiment, inconsideration of the possibility that a large torque variation may begenerated if the correction amount of the fuel injection quantity islarge, when it is determined in Step 700 that the calculated correctionamount of the fuel injection quantity is small, the control apparatusindividually corrects the fuel injection quantity in each of thecylinders Nos. 1 through 4 in Step 505, thereby minimizing the variationin the air-fuel ratio among the cylinders. On the other hand, when it isdetermined in Step 700 that the calculated correction amount of the fuelinjection quantity is large, the correction amount of the fuel injectionquantity is guarded by a predetermined value in Step 701. A correctedtarget air-fuel ratio is then calculated in Steps 602 and 603 and thefuel injection quantity of all of the cylinders Nos. 1 through 4 areuniformly corrected by that corrected target air-fuel ratio in Step 604.That is, air-fuel ratio feedback control is performed, such that torquevariation is reduced while the air-fuel ratio is able to beappropriately controlled.

The aforementioned eighth, ninth and tenth embodiments may be appliednot only in the case in which the valve lift amount of the intake valve2 is set as shown by the solid line in FIG. 6, but also in the case inwhich the valve lift amount of the intake valve 2 is set as shown by thechain line in FIG. 6, as well as in the case in which the closing timingof the intake valve 2 is retarded.

According to the invention, by making the throttle valve opening amountin one cylinder when the exhaust gas air-fuel ratio of that cylinder iscalculated and the throttle valve opening amount in another cylinderwhen the exhaust gas air-fuel ratio of that cylinder is calculatedsubstantially the same, the intake air amount introduced into the onecylinder when the exhaust gas air-fuel ratio of that cylinder iscalculated and the intake air amount introduced into the other cylinderwhen the exhaust gas air-fuel ratio of that cylinder is calculated areable to made the same. Furthermore, while a variation in the air-fuelratio among cylinders can be reduced just as in the control apparatusfor a multi-cylinder internal combustion engine disclosed in JapanesePatent Application Laid-Open Publication No. 6-213044, a pulsationgenerated by a variation in torque among cylinders when there is avariation in fuel injection quantity among cylinders can be avoided.That is, a variation in air-fuel ratio among cylinders as well as avariation in torque among cylinders can be reduced.

According to an aspect of the invention, a variation in the intake airamount among cylinders can be reduced without generating a variation intorque among cylinders even if there is a variation in the fuelinjection quantity between cylinders.

According to another aspect of the invention, a variation in the intakeair amount between cylinders can be minimized without generating avariation in torque between cylinders even if there is a variation inthe fuel injection quantity between cylinders.

According to another aspect of the invention, a variation in theoperation angle of the intake valve among cylinders can be reducedwithout generating a variation in torque among cylinders even if thereis a variation in the fuel injection quantity among cylinders.

According to another aspect of the invention, by using a neural network,a variation among cylinders can be reduced more effectively than withoutusing a neural network.

According to another aspect of the invention, a variation in theair-fuel ratio between cylinders is able to be controlled moreappropriately than with the control apparatus for a multi-cylinderinternal combustion engine disclosed in Japanese Patent ApplicationLaid-Open Publication No. 6-213044, in which a variation betweencylinders is not able to be minimized based on the amount of valveoverlap of the intake valve and the exhaust valve, when the amount ofvalve overlap of the intake valve and the exhaust valve is able to bechanged. In other words, it is possible to appropriately control thevariation in the air-fuel ratio among the cylinders.

According to another aspect of the invention, a variation in theair-fuel ratio among cylinders can be controlled more appropriately thanwith the control apparatus for a multi-cylinder internal combustionengine disclosed in Japanese Patent Application Laid-Open PublicationNo. 6-213044, in which a variation among cylinders cannot be reducedbased on the operation angle of the intake valve, when the operationangle of the intake valve can be changed. In other words, it is possibleto appropriately control the variation in the air-fuel ratio among thecylinders.

According to another aspect of the invention, a variation in theair-fuel ration between cylinders is able to be controlled moreappropriately than when the fuel injection quantity is not able to becorrected based on the operation angle of the intake valve.

According to another aspect of the invention, a value of the targetair-fuel ratio can be set to a more appropriate value than when thetarget air-fuel ratio is not able to be corrected by the operation angleof the intake valve. That is, the control apparatus is capable ofexecuting appropriate air-fuel ratio feedback control even when a sensoris not sufficiently exposed to the exhaust gas, i.e., even when a targetair-fuel ratio calculated from a value output by a sensor is not anappropriate target air-fuel ratio.

According to another aspect of the invention, a variation in air-fuelratio among cylinders as well as a variation in torque among cylinderscan be minimized.

While the invention has been described with reference to preferredembodiments thereof, it is to be understood that the invention is notlimited to the preferred embodiments or constructions. To the contrary,the invention is intended to cover various modifications and equivalentarrangements. In addition, while the various elements of the preferredembodiments are shown in various combinations and configurations, whichare exemplary, other combinations and configurations, including more,less or only a single element, are also within the spirit and scope ofthe invention.

1. A control apparatus for a multi-cylinder internal combustion engineincluding a plurality of cylinders, the control apparatus comprising acontroller that: calculates an exhaust gas air-fuel ratio of a cylinderwhen valve opening characteristics of an intake valve and an exhaustvalve of each of the cylinders of the internal combustion engine are setsuch that an amount of an intake air introduced into the cylinder is notlimited by the valve opening characteristics; and reduces a variation ina fuel injection quantity among the plurality of cylinders on the basisof the calculated exhaust gas air-fuel ratio of each of the cylinders.2. A control apparatus according to claim 1, wherein the controllercalculates the exhaust gas air-fuel ratio of each of the cylinders whenthe valve opening characteristics of the intake valve and the exhaustvalve of each cylinder are set such that the amount of the intake airintroduced into each cylinder of the internal combustion engine islimited by a throttle valve opening amount.
 3. A control apparatusaccording to claim 1, wherein the controller: calculates the exhaust gasair-fuel ratio of the cylinder when the valve opening characteristics ofthe intake valve and the exhaust valve are set such that the amount ofthe intake air introduced into the cylinder is limited by the valveopening characteristics after reducing the variation in the fuelinjection quantity among the plurality of cylinders; and reduces avariation in the valve opening characteristics of the intake valve andthe exhaust valve among the plurality of cylinders on the basis of thecalculated exhaust gas air-fuel ratio of the cylinder.
 4. A controlapparatus according to claim 3, wherein the controller calculates theexhaust gas air-fuel ratio of the cylinder when the valve openingcharacteristics of the intake valve and the exhaust valve are set suchthat the amount of the intake air introduced into the cylinder is notlimited by a throttle valve opening amount, but is limited by the valveopening characteristics of the intake valve and the exhaust valve afterreducing the variation in the fuel injection quantity among theplurality of cylinders.
 5. A control apparatus according to claim 1,wherein a neural network is used to reduce the variation among theplurality of cylinders.
 6. A control apparatus for a multi-cylinderinternal combustion engine including a plurality of cylinders, thecontrol apparatus comprising a controller that: calculates an exhaustgas air-fuel ratio of each of the cylinders when an operation angle ofan intake valve of each cylinder of the internal combustion engine isset to a predetermined angle; and reduces a variation in a fuelinjection quantity among the plurality of cylinders on the basis of thecalculated exhaust gas air-fuel ratio of each of the cylinders.
 7. Acontrol apparatus according to claim 6, wherein the controllercalculates the exhaust gas air-fuel ratio of each of the cylinders whenthe operation angle of the intake valve is set such that an amount ofintake air introduced into a cylinder of the internal combustion engineis not limited by the operation angle of the intake valve.
 8. A controlapparatus according to claim 7, wherein the controller calculates theexhaust gas air-fuel ratio of each of the cylinders when the amount ofthe intake air introduced into each cylinder of the internal combustionengine is not limited by the operation angle of the intake valve, but islimited by a throttle valve opening amount.
 9. A control apparatusaccording to claim 6, wherein the controller calculates the exhaust gasair-fuel ratio of each of the cylinders when the operation angle of theintake valve is set to a maximum operation angle.
 10. A controlapparatus according to claim 6, wherein the controller: calculates theexhaust gas air-fuel ratio of each of the cylinders when valve openingcharacteristics of the intake valve and an exhaust valve are set suchthat an amount of intake air introduced into each of the cylinders islimited by the valve opening characteristics after reducing thevariation in the fuel injection quantity among the plurality ofcylinders; and reduces a variation in the valve opening characteristicsof the intake valve and the exhaust valve among the plurality ofcylinders on the basis of the calculated exhaust gas air-fuel ratio ofeach of the cylinders.
 11. A control apparatus according to claim 6,wherein the controller: calculates the exhaust gas air-fuel ratio ofeach of the cylinders when the operation angle of the intake valve isset to an operation angle that is smaller than the predetermined angleafter reducing the variation in the fuel injection quantity among theplurality of cylinders; and reduces a variation in the amount of theintake air among the plurality of cylinders on the basis of thecalculated exhaust gas air-fuel ratio of each of the cylinders.
 12. Acontrol apparatus according to claim 6, wherein the controller:calculates the exhaust gas air-fuel ratio of each of the cylinders whenthe operation angle of the intake valve is set to an operation anglethat is smaller than the predetermined angle after reducing thevariation in the fuel injection quantity among the plurality ofcylinders; and reduces a variation in the operation angle of the intakevalve among the cylinders on the basis of the calculated exhaust gasair-fuel ratio of each of the cylinders.
 13. A control apparatus for amulti-cylinder internal combustion engine, the control apparatuscomprising a controller that: calculates an exhaust gas air-fuel ratioof each of the cylinders when a valve overlap amount of an intake valveand an exhaust valve of each of the cylinders of the internal combustionengine is set to a predetermined amount; and reduces a variation in afuel injection quantity among the plurality of cylinders on the basis ofthe calculated exhaust gas air-fuel ratio of each of the cylinders. 14.A control apparatus according to claim 13, wherein the controllercalculates the exhaust gas air-fuel ratio of each of the cylinders whenthe valve overlap amount of the intake valve and the exhaust valve isset such that an amount of the intake air introduced into each of thecylinders is not limited by the valve overlap amount.
 15. A controlapparatus according to claim 14, wherein the controller calculates theexhaust gas air-fuel ratio of each of the cylinders when the valveoverlap amount of the intake valve and the exhaust valve is set suchthat the amount of the intake air introduced into each of the cylindersis not limited by the valve overlap amount, but is limited by a throttlevalve opening amount.
 16. A control apparatus according to claim 13,wherein the controller calculates the exhaust gas air-fuel ratio of eachof the cylinders when the valve overlap amount of the intake valve andthe exhaust valve is set to a minimum amount.
 17. A method ofcontrolling a multi-cylinder internal combustion engine including aplurality of cylinders, comprising the steps of: calculating an exhaustgas air-fuel ratio of a cylinder when valve opening characteristics ofan intake valve and an exhaust valve of each of the cylinders of theinternal combustion engine are set such that an amount of an intake airintroduced into the cylinder is not limited by the valve openingcharacteristics; and reducing a variation in a fuel injection quantityamong the plurality of cylinders on the basis of the calculated exhaustgas air-fuel ratio of each of the cylinders.
 18. A method of controllinga multi-cylinder internal combustion engine including a plurality ofcylinders, comprising the steps of: calculating an exhaust gas air-fuelratio of each of the cylinders when an operation angle of an intakevalve of each of the cylinders of the internal combustion engine is setto a predetermined angle; and reducing a variation in a fuel injectionquantity among the plurality of cylinders on the basis of the calculatedexhaust gas air-fuel ratio of each of the cylinders.
 19. A method ofcontrolling a multi-cylinder internal combustion engine including aplurality of cylinders, comprising the steps of: calculating an exhaustgas air-fuel ratio of each of the cylinders when a valve overlap amountof an intake valve and an exhaust valve of each of the cylinders of theinternal combustion engine is set to a predetermined amount; andreducing a variation in a fuel injection quantity among the plurality ofcylinders on the basis of the calculated exhaust gas air-fuel ratio ofeach of the cylinders.